[Github] Add github-automation container (#200704)

There are several jobs that use the pattern:
1. Checkout github-automation.py script.
2. Install dependencies for github-automation.py script.
3. Run the github-automation.py script.

We can consolidate a lot of this logic into the container and simplify
the workflows. This may also speed them up the workflow jobs slightly,
but most of them are already pretty fast, so it may not make a big
difference.

.github/workflows/build-ci-container-tooling.yml

@@ -10,6 +10,7 @@ on:
     paths:
       - .github/workflows/build-ci-container-tooling.yml
       - '.github/workflows/containers/github-action-ci-tooling/**'
+      - llvm/utils/git/github-automation.py
       - llvm/utils/git/requirements_formatting.txt
       - llvm/utils/git/requirements_linting.txt
       - '.github/actions/build-container/**'
@@ -18,6 +19,7 @@ on:
     paths:
       - .github/workflows/build-ci-container-tooling.yml
       - '.github/workflows/containers/github-action-ci-tooling/**'
+      - llvm/utils/git/github-automation.py
       - llvm/utils/git/requirements_formatting.txt
       - llvm/utils/git/requirements_linting.txt
       - '.github/actions/build-container/**'
@@ -39,6 +41,11 @@ jobs:
           - container-name: abi-tests
             test-command: 'cd $HOME && abi-compliance-checker --help'
             target: abi-tests
+          - container-name: github-automation
+            test-command: 'true'
+            target: github-automation
+            context: llvm/utils/git/
+
     steps:
       - name: Checkout LLVM
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
@@ -48,6 +55,7 @@ jobs:
             .github/workflows/containers/github-action-ci-tooling/
             llvm/utils/git/requirements_formatting.txt
             llvm/utils/git/requirements_linting.txt
+            llvm/utils/git/github-automation.py
             clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py
             .github/actions/build-container
 
@@ -58,6 +66,7 @@ jobs:
           dockerfile: .github/workflows/containers/github-action-ci-tooling/Dockerfile
           target: ci-container-${{ matrix.target || format('code-{0}', matrix.container-name) }}
           test-command: ${{ matrix.test-command }}
+          context: ${{ matrix.context }}
 
   push-ci-container:
     if: github.event_name == 'push'

.github/workflows/containers/github-action-ci-tooling/Dockerfile

@@ -113,3 +113,16 @@ RUN apt-get update && \
     universal-ctags && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*
+
+FROM base as ci-container-github-automation
+
+RUN apt-get update && \
+    DEBIAN_FRONTEND=noninteractive apt-get install -y \
+    python3-git \
+    python3-github && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/*
+
+USER gha
+
+ADD github-automation.py /usr/local/bin/