Add developer documentation for the Federation Sender and add a documentation mechanism using Sphinx. (#15265)

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

.github/workflows/docs.yaml

@@ -13,25 +13,10 @@ on:
   workflow_dispatch:
 
 jobs:
-  pages:
-    name: GitHub Pages
+  pre:
+    name: Calculate variables for GitHub Pages deployment
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-
-      - name: Setup mdbook
-        uses: peaceiris/actions-mdbook@adeb05db28a0c0004681db83893d56c0388ea9ea # v1.2.0
-        with:
-          mdbook-version: '0.4.17'
-
-      - name: Build the documentation
-        # mdbook will only create an index.html if we're including docs/README.md in SUMMARY.md.
-        # However, we're using docs/README.md for other purposes and need to pick a new page
-        # as the default. Let's opt for the welcome page instead.
-        run: |
-          mdbook build
-          cp book/welcome_and_overview.html book/index.html
-
       # Figure out the target directory.
       #
       # The target directory depends on the name of the branch
@@ -55,11 +40,65 @@ jobs:
 
           # finally, set the 'branch-version' var.
           echo "branch-version=$branch" >> "$GITHUB_OUTPUT"
-          
+    outputs:
+      branch-version: ${{ steps.vars.outputs.branch-version }}
+
+################################################################################
+  pages-docs:
+    name: GitHub Pages
+    runs-on: ubuntu-latest
+    needs:
+      - pre
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup mdbook
+        uses: peaceiris/actions-mdbook@adeb05db28a0c0004681db83893d56c0388ea9ea # v1.2.0
+        with:
+          mdbook-version: '0.4.17'
+
+      - name: Build the documentation
+        # mdbook will only create an index.html if we're including docs/README.md in SUMMARY.md.
+        # However, we're using docs/README.md for other purposes and need to pick a new page
+        # as the default. Let's opt for the welcome page instead.
+        run: |
+          mdbook build
+          cp book/welcome_and_overview.html book/index.html
+
       # Deploy to the target directory.
       - name: Deploy to gh pages
         uses: peaceiris/actions-gh-pages@bd8c6b06eba6b3d25d72b7a1767993c0aeee42e7 # v3.9.2
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./book
-          destination_dir: ./${{ steps.vars.outputs.branch-version }}
+          destination_dir: ./${{ needs.pre.outputs.branch-version }}
+
+################################################################################
+  pages-devdocs:
+    name: GitHub Pages (developer docs)
+    runs-on: ubuntu-latest
+    needs:
+      - pre
+    steps:
+      - uses: action/checkout@v3
+
+      - name: "Set up Sphinx"
+        uses: matrix-org/setup-python-poetry@v1
+        with:
+          python-version: "3.x"
+          poetry-version: "1.3.2"
+          groups: "dev-docs"
+          extras: ""
+
+      - name: Build the documentation
+        run: |
+          cd dev-docs
+          poetry run make html
+
+      # Deploy to the target directory.
+      - name: Deploy to gh pages
+        uses: peaceiris/actions-gh-pages@bd8c6b06eba6b3d25d72b7a1767993c0aeee42e7 # v3.9.2
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./dev-docs/_build/html
+          destination_dir: ./dev-docs/${{ needs.pre.outputs.branch-version }}