Get GitHub repo setup variables from templates

Different templates have different methods for determining the GitHub
repo name and organization. Initially we do this with a series of cases,
but we might want to refactor this or make it more systematic to better
allow new templates to reliably set their intended github repo without
needing to modify this code.

src/templatebot/services/template.py

@@ -146,6 +146,13 @@ async def create_project_from_template(
         trigger_channel_id: str | None,
     ) -> None:
         """Create a GitHub repository and set up a project from a template."""
+        # Values for the repository creation. We'll set this when possible
+        # during the pre-processing steps.
+        github_owner: str | None = None
+        github_name: str | None = None
+        github_homepage_url: str | None = None
+        github_description: str | None = None
+
         # Preprocessing steps. First convert values from the Slack modal into
         # cookiecutter template variables. This expands the templatekit
         # preset_groups and preset_options into the full set of template
@@ -158,14 +165,77 @@ async def create_project_from_template(
         # present.
         await self._expand_author_id_variable(template_values)
 
-        # Handle repository/serial number assignment for technotes
         if template.name.startswith("technote_"):
+            # Handle preprocessing steps for technotes. These have
+            # automatically assigned repository/serial numbers
             await self._assign_technote_repo_serial(template_values)
+            github_owner = template_values["github_org"]
+            github_name = (
+                f"{template_values['series'].lower()}"
+                f"-{template_values['serial_number']}"
+            )
+            github_homepage_url = f"https://{github_name}.lsst.io/"
+            github_description = template_values["title"]
+
+        elif template.name == "latex_lsstdoc":
+            # Preprocessing steps for change control documents hosted in
+            # docushare. These have manually-assigned serial numbers.
+            #
+            # In the latex_lsstdoc template, the series and serial_number are
+            # determined from the handle, which the author enters.
+            # This logic attempts to match this metadata
+            # and extract it, if necessary and possible.
+            handle = template_values["handle"]
+            handle_match = re.match(
+                r"(?P<series>[A-Z]+)-(?P<serial_number>[0-9]+)", handle
+            )
+            if handle_match is None:
+                # If the handle does not match the expected pattern, then
+                # we cannot determine the series and serial number.
+                # TODO(jonathansick): send a Slack message to the user
+                raise ValueError(
+                    f"Cannot determine series and serial number from handle: "
+                    f"{handle}"
+                )
+            template_values["series"] = handle_match["series"]
+            template_values["serial_number"] = handle_match["serial_number"]
+            github_owner = template_values["github_org"]
+            github_name = handle.lower()
+            github_homepage_url = f"https://{github_name}.lsst.io/"
+            github_description = template_values["title"]
+
+        elif template.name == "test_report":
+            # In test_report templates the series and serial_number are
+            # manually assigned.
+            github_name = (
+                f"{template_values['series'].lower()}-"
+                f"{template_values['serial_number']}"
+            )
+            github_owner = template_values["github_org"]
+            github_homepage_url = f"https://{github_name}.lsst.io/"
+            github_description = template_values["title"]
+
+        else:
+            # A generic repository template. By definition the "name"
+            # is treated as teh github repo name, and the "github_org"
+            # is the owner.
+            github_name = template_values["name"]
+            github_owner = template_values["github_org"]
+            if "summary" in template_values:
+                github_description = template_values["summary"]
+            elif "description" in template_values:
+                github_description = template_values["description"]
 
         # Create a Markdown code block showing the template variable names
         # and the assigned values
         assignment_lines = [
-            f"- `{key}` = `{value}`" for key, value in template_values.items()
+            f"* `{key}` = `{value}`" for key, value in template_values.items()
+        ]
+        github_variables = [
+            f"* github_name = `{github_name}`",
+            f"* github_owner = `{github_owner}`",
+            f"* github_homepage_url = `{github_homepage_url}`",
+            f"* github_description = `{github_description}`",
         ]
         text_block = SlackSectionBlock(
             fields=[
@@ -178,6 +248,9 @@ async def create_project_from_template(
                 SlackMrkdwnTextObject(
                     text=f"Template values:\n\n{'\n'.join(assignment_lines)}"
                 ),
+                SlackMrkdwnTextObject(
+                    text=f"GitHub values:\n\n{'\n'.join(github_variables)}"
+                ),
             ]
         )
         if trigger_channel_id and trigger_message_ts:
@@ -290,7 +363,13 @@ async def _expand_author_id_variable(
     async def _assign_technote_repo_serial(
         self, template_values: dict[str, str]
     ) -> None:
-        """Assign a repository serial number for a technote."""
+        """Assign a repository serial number for a technote and update the
+        template values.
+
+        The following standard technote template values are updated:
+
+        - ``serial_number``
+        """
         org_name = template_values["github_org"]
         series = template_values["series"].lower()