Fix web-docs.element.dev deployment (#32922)

* Fix docs

* Switch to vitepress for doc generation

* Run doc build in CI

* Switch docs build to layered

.gitignore

@@ -16,7 +16,6 @@ package-lock.json
 .env
 .env.*
 coverage
-/book
 /index.html
 # version file and tarball created by `npm pack` / `yarn pack`
 /git-revision.txt
@@ -38,3 +37,7 @@ storybook-static
 .nx/workspace-data
 
 .pnpm-store
+
+# vitepress
+/docs/.vitepress/dist
+/docs/.vitepress/cache