chore: Add templates for PRs and automated release notes

.github/ISSUE_TEMPLATE/bug-report.yml

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+name: Bug report
+description: Report something that is broken
+labels: ["bug"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for taking the time to fill out this bug report!
+
+        Note that since Altair is a Python wrapper around the Vega-Lite visualization grammar, [most bugs should be reported directly to Vega-Lite](https://github.com/vega/vega-lite/issues). You can click the Action Button (`...`) of your Altair chart and "Open in Vega Editor" to see if you get the same error in the Vega Editor.
+
+        If you can't reproduce the bug in the Vega Editor, then make sure you are using [the latest version of Altair](https://github.com/altair-viz/altair/releases) and search for duplicate issues before filling out the form below.
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: What happened?
+      description: |
+        Describe what happened and how to reproduce the bug.
+        Include the full code and data to reproduce it. Use a simple toy data set, e.g. from `vega_datasets`.
+    validations:
+      required: true
+  - type: textarea
+    id: desired-behavior
+    attributes:
+      label: What would you like to happen instead?
+      description: Describe the expected/desired behavior.
+  - type: input
+    id: altair-version
+    attributes:
+      label: Which version of Altair are you using?
+      description: Use `alt.__version__` to find out
+  - type: markdown
+    attributes:
+      value: By submitting this issue, you agree to follow our [Code of Conduct](../../CODE_OF_CONDUCT.md).

.github/ISSUE_TEMPLATE/feature-request.yml

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+name: Feature request
+description: Suggest an improvement
+labels: ["enhancement"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Thanks for taking the time to suggest a new feature!
+
+        Note that since Altair is a Python wrapper around the Vega-Lite visualization grammar, [most feature requests should be reported directly to Vega-Lite](https://github.com/vega/vega-lite/issues). You can click the Action Button (`...`) of your Altair chart and "Open in Vega Editor" to see the Vega-Lite chart specification.
+
+        If you believe this feature is more relevant for Altair than Vega-Lite, then make sure to search for duplicate issues before filling out the form below.
+  - type: textarea
+    id: what-happened
+    attributes:
+      label: What is your suggestion?
+      description: Describe the feature's goal, motivating use cases, and its expected behavior.
+    validations:
+      required: true
+  - type: textarea
+    id: alternative-solutions
+    attributes:
+      label: Have you considered any alternative solutions?
+  - type: markdown
+    attributes:
+      value: By submitting this issue, you agree to follow our [Code of Conduct](../../CODE_OF_CONDUCT.md).

.github/pull_request_template.md

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+<!-- Click "Preview" to read this message; then delete it. -->
+
+Thanks for contributing to Altair!
+
+Please follow these guidelines when submitting your PR:
+
+- Describe the purpose of the changes in PR, so that it is easy to understand the implication of the suggested changes.
+    - Here is a [helpful article about writing effective PR descriptions](https://medium.com/@greenberg/writing-pull-requests-your-coworkers-might-enjoy-reading-9d0307e93da3).
+- Include unit tests and documentation for new features
+- Ensure that the title is a concise [semantic commit message](https://www.conventionalcommits.org/) (e.g. "feat: Add `embed_options` to charts").
+    - Append `!` if the change is breaking (e.g. "fix!: Raise error when `embed_options` is `None`")

.github/release.yml

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+changelog:
+  categories:
+    - title: Enhancements
+      labels:
+        - enhancement
+    - title: Bug Fixes
+      labels:
+        - bug
+    - title: Maintainance
+      labels:
+        - maintainance
+    - title: Documentation
+      labels:
+        - documentation
+    - title: Other Changes
+      labels:
+        - "*"

.github/workflows/check-pr.yml

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+name: "Lint PR"
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - edited
+      - synchronize
+
+permissions:
+  pull-requests: read
+
+jobs:
+  main:
+    name: Validate PR title
+    runs-on: ubuntu-latest
+    steps:
+      - uses: amannn/action-semantic-pull-request@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}