Pin workflows to fix zizmor (#537)

Also removes the dependabot.yml as it is not needed anymore. Renovate
will update the plugin sdk go.

Author: zoltanbedi

.github/dependabot.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - id: get-github-token
-        uses: grafana/shared-workflows/actions/create-github-app-token@create-github-app-token/v0.2.2
+        uses: grafana/shared-workflows/actions/create-github-app-token@ae92934a14a48b94494dbc06d74a81d47fe08a40 # create-github-app-token/v0.2.2
         with:
           github_app: grafana-oss-big-tent
       - name: Add to project

.github/workflows/add-to-project.yml

@@ -15,9 +15,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - id: get-github-token
-        uses: grafana/shared-workflows/actions/create-github-app-token@create-github-app-token/v0.2.2
+        uses: grafana/shared-workflows/actions/create-github-app-token@ae92934a14a48b94494dbc06d74a81d47fe08a40 # create-github-app-token/v0.2.2
         with:
           github_app: grafana-oss-big-tent
-      - uses: grafana/plugin-actions/create-plugin-update@create-plugin-update/v2.0.1
+      - uses: grafana/plugin-actions/create-plugin-update@244c3bc9c6eb94bc1dd6458ade2462499bbf0f5b #create-plugin-update/v2.0.1
         with:
           token: ${{ steps.get-github-token.outputs.token }}