doc: add versioning using "mike"

The Python tool 'mike'[1] helps manage multiple versions of MkDocs-powered
documentation.  Only required when building the kernelkit.org site docs!

For each new tag, that steps year or month, a new version of is created of
the documentation, in a separate sub-directory on the gh-pages branch.

Strategy - Version Grouping with Early Publishing:

- Extract YEAR.MONTH from tag
  E.g., v25.06.0-beta1, v25.06.0-rc1, v25.06.0, v25.06.1 → become version 25.06
- From first pre-release onwards:
  - v25.06.0-beta1 → creates docs version 25.06
  - v25.06.0-rc1 → updates docs version 25.06
  - v25.06.0 (GA) → updates docs version 25.06
  - v25.06.1 (patch) → updates docs version 25.06
- New major/minor series:
  - v25.07.0-beta1 → creates new docs version 25.07

Benefits:
 - Users get docs as soon as beta/rc is available
 - Patches update existing docs (logical since patches rarely change docs significantly)
 - Clean version grouping by YEAR.MONTH
 - Mike handles create vs update automatically

[1]: https://github.com/jimporter/mike

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

.github/workflows/docs.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - doc
+      - main
+    tags:
+      - 'v*'
     paths:
       - 'doc/**'
       - 'mkdocs.yml'
@@ -16,22 +19,20 @@ on:
       - '.github/workflows/docs.yml'
 
 permissions:
-  contents: read
-  pages: write
-  id-token: write
+  contents: write
 
 concurrency:
-  group: "pages"
+  group: "docs-${{ github.ref }}"
   cancel-in-progress: false
 
 jobs:
-  build:
+  docs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
         with:
-          fetch-depth: 0  # Needed for git-revision-date-localized plugin
+          fetch-depth: 0
 
       - name: Setup Python
         uses: actions/setup-python@v4
@@ -44,23 +45,28 @@ jobs:
           pipx inject mkdocs mkdocs-material
           pipx inject mkdocs pymdown-extensions
           pipx inject mkdocs mkdocs-callouts
+          pipx inject mkdocs mike
+          # Workaround, if pipx inject fails to install symlink
+          ln -s "$(pipx environment -V PIPX_LOCAL_VENVS)/mkdocs/bin/mike" \
+                "$(pipx environment -V PIPX_BIN_DIR)/mike" || true
 
-      - name: Build documentation
-        run: mkdocs build
+      - name: Configure Git
+        run: |
+          git config --global user.name "github-actions[bot]"
+          git config --global user.email "github-actions[bot]@users.noreply.github.com"
 
-      - name: Upload Pages artifact
-        uses: actions/upload-pages-artifact@v3
-        with:
-          path: site/
+      - name: Deploy dev version
+        if: github.event_name == 'push' && (github.ref == 'refs/heads/doc' || github.ref == 'refs/heads/main')
+        run: |
+          mike deploy --push --update-aliases dev latest
+          mike set-default --push latest
 
-  deploy:
-    if: github.ref == 'refs/heads/doc' && github.event_name == 'push'
-    needs: build
-    runs-on: ubuntu-latest
-    environment:
-      name: github-pages
-      url: ${{ steps.deployment.outputs.page_url }}
-    steps:
-      - name: Deploy to GitHub Pages
-        id: deployment
-        uses: actions/deploy-pages@v4
+      - name: Deploy tagged version
+        if: github.event_name == 'push' && startsWith(github.ref, 'refs/tags/v')
+        run: |
+          TAG=${GITHUB_REF#refs/tags/v}
+          # Extract YEAR.MONTH from tag (e.g., v25.06.0-beta1 -> 25.06)
+          VERSION=$(echo $TAG | sed -E 's/^([0-9]+\.[0-9]+)(\.[0-9]+)?(-.*)?$/\1/')
+          echo "Deploying tag $TAG as docs version $VERSION"
+          mike deploy --push --update-aliases $VERSION latest
+          mike set-default --push latest

mkdocs.yml

@@ -110,7 +110,10 @@ markdown_extensions:
 plugins:
   - search
   - callouts
+  - mike
 
 extra:
   generator: false
   homepage: https://kernelkit.org/
+  version:
+    provider: mike