Fixing documentation push permissions (#388)

The default GITHUB_TOKEN should have proper permissions to push to
the gh-pages branch, the ROBOT_TOKEN is deprecated.

.github/workflows/docs.yaml

@@ -1,13 +1,14 @@
 name: Docs
 on:
+  workflow_dispatch: {}
   push:
     branches:
       - main
     paths:
       - "documentation/**"
 
 permissions:
-  contents: read
+  contents: write
 
 jobs:
   release:
@@ -26,16 +27,6 @@ jobs:
         with:
           python-version: "3.x"
 
-      - name: Configure git
-        env:
-          ROBOT_TOKEN: ${{ secrets.ROBOT_TOKEN }}
-        run: |
-          git config --global url."https://percona-platform-robot:${ROBOT_TOKEN}@github.com".insteadOf "https://github.com"
-          git config user.name "GitHub Action"
-          git config user.email "[email protected]"
-          git config user.password "${ROBOT_TOKEN}"
-          echo "GIT_USER=percona-platform-robot:${ROBOT_TOKEN}" >> $GITHUB_ENV
-
       - name: Install MkDocs
         run: |
           python -m pip install --upgrade pip