Add docs migration warning and redirects from old pages

Closes #932

CHANGES/932.misc

@@ -0,0 +1 @@
+Added warning about the new docs location on the legacy docs and included some redirects.

docs/index.md

@@ -0,0 +1,8 @@
+# Pulp 3 CLI Docs
+
+The documentation for pulp-cli and pulp-glue has moved to a new place.
+
+Learn more about the new documentation project [here](https://discourse.pulpproject.org/t/unified-documentation-part-2/1188/2) or go to the new site:
+
+- [pulp-cli section](https://staging-docs.pulpproject.org/pulp-cli/docs/user/)
+- [pulp-glue section](https://staging-docs.pulpproject.org/pulp-glue/docs/dev/learn/architecture/)

mkdocs.yml

@@ -17,39 +17,20 @@ markdown_extensions:
   - "pymdownx.tabbed":
       alternate_style: false
 plugins:
-  - "search"
-  - mkdocstrings:
-      default_handler: "python"
-      handlers:
-        python:
-          paths:
-            - "pulp-glue/pulp_glue"
-            - "pulp-glue"
-          options:
-            heading_level: 2
-            show_root_heading: false
-            show_root_toc_entry: false
-            show_symbol_type_heading: true
-            show_if_no_docstring: false
-            show_signature_annotations: true
-            separate_signature: true
-            members_order: "source"
-            merge_init_into_class: true
+  - redirects:
+      redirect_maps:
+        "installation.md": "index.md"
+        "configuration.md": "index.md"
+        "using_the_cli.md": "index.md"
+        "supported_workflows.md": "index.md"
+        "advanced_features.md": "index.md"
+        "CHANGES.md": "index.md"
+        "contributing.md": "index.md"
+        "architecture.md": "index.md"
+        "glue_reference/common_openapi.md": "index.md"
+        "glue_reference/common_context.md": "index.md"
+        "glue_reference/common_i18n.md": "index.md"
+        "glue_reference/core_context.md": "index.md"
+        "cli_reference/common_generic.md": "index.md"
 nav:
   - "Overview": "index.md"
-  - "installation.md"
-  - "configuration.md"
-  - "using_the_cli.md"
-  - "supported_workflows.md"
-  - "advanced_features.md"
-  - "CHANGES.md"
-  - "Developer material":
-    - "contributing.md"
-    - "architecture.md"
-  - "Pulp Glue API Reference":
-    - "glue_reference/common_openapi.md"
-    - "glue_reference/common_context.md"
-    - "glue_reference/common_i18n.md"
-    - "glue_reference/core_context.md"
-  - "Pulp CLI plumbings API Reference":
-    - "cli_reference/common_generic.md"