docs: Move to mkdocs-material, port Helm to docs site

This supersedes https://github.com/kata-containers/kata-containers/pull/12622.
I replaced Zensical with mkdocs-materialx. Materialx is a fork of mkdocs-material
created after mkdocs-material was put into maintenance mode. We'll use this
platform until Zensical is more feature complete.

Added a few of the existing docs into the site to make a more user-friendly flow.

Signed-off-by: LandonTClipp <11232769+LandonTClipp@users.noreply.github.com>

.github/workflows/docs.yaml

@@ -4,17 +4,18 @@ on:
     branches:
       - main
 permissions: {}
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
-  deploy-docs:
-    name: deploy-docs
+  build:
+    runs-on: ubuntu-24.04
+    name: Build docs
     permissions:
       contents: read
       pages: write
       id-token: write
-    environment:
-      name: github-pages
-      url: ${{ steps.deployment.outputs.page_url }}
-    runs-on: ubuntu-latest
     steps:
       - uses: actions/configure-pages@983d7736d9b0ae728b81ab479565c72886d7745b # v5.0.0
       - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
@@ -23,10 +24,30 @@ jobs:
       - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5.6.0
         with:
           python-version: 3.x
-      - run: pip install zensical
-      - run: zensical build --clean
+
+      - run: pip install -r docs/requirements.txt
+      - run: python3 -m mkdocs build --config-file ./mkdocs.yaml --site-dir site/
+        id: build
+
       - uses: actions/upload-pages-artifact@7b1f4a764d45c48632c6b24a0339c27f5614fb0b # v4.0.0
-        with:
-          path: site
-      - uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e # v4.0.5
         id: deployment
+        with:
+          path: site/
+          name: github-pages
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-24.04
+    name: Deploy docs
+    permissions:
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e # v4.0.5
+        id: deployment
+        with:
+          artifact_name: github-pages