feat(docker): add Docker Hub authentication for CI/CD workflows

- Introduced `docker_hub_token` and `docker_hub_username` secrets for Docker Hub login in CI/CD workflows.
- Updated `.gitea/workflows/ci.yaml`, `.gitea/workflows/cd.yaml`, and `.gitea/workflows/quality.yaml` to utilize these secrets for Docker Hub authentication.
- Enhanced README and releasing documentation to clarify the use of Docker Hub credentials for image mirroring and builds.

.gitea/workflows/quality.yaml

@@ -26,6 +26,10 @@ on:
     secrets:
       ACTIONS_PAT:
         required: false
+      docker_hub_token:
+        required: false
+      docker_hub_username:
+        required: false
 
 permissions:
   contents: read
@@ -397,6 +401,12 @@ jobs:
           name: evobgp
           driver: docker-container
           cleanup: false
+      - name: Log in to Docker Hub
+        if: secrets.docker_hub_token != ''
+        uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772 # v3.4.0
+        with:
+          username: ${{ secrets.docker_hub_username || gitea.actor }}
+          password: ${{ secrets.docker_hub_token }}
       - name: Log in to Gitea Registry
         if: inputs.allow_registry_login
         uses: docker/login-action@74a5d142397b4f367a81961eba4e8cd7edddf772 # v3.4.0