refactor: rename Gitea environment variables to CI registry prefix

update SETUP.md and .env.example

.gitea/workflows/ci.yml

@@ -63,8 +63,8 @@ jobs:
         uses: docker/login-action@v3
         with:
           registry: git.allucanget.biz
-          username: ${{ secrets.GITEA_USERNAME }}
-          password: ${{ secrets.GITEA_TOKEN }}
+          username: ${{ secrets.CI_REGISTRY_USER }}
+          password: ${{ secrets.CI_REGISTRY_TOKEN }}
 
       - name: Extract metadata for Playout
         id: meta-playout
@@ -169,4 +169,4 @@ jobs:
         with:
           generate_release_notes: true
         env:
-          GITHUB_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.CI_REGISTRY_TOKEN }}