feat(docker): enable relative path support for Docker bake configurations

- Added `BUILDX_BAKE_FILE_RELATIVE_PATHS` environment variable to CI workflows to support relative paths in Docker bake commands.
- Updated `docker-bake.hcl` comments to clarify context resolution from the current working directory.
- Revised README documentation to reflect changes in context resolution and usage of the new environment variable.

.gitea/workflows/cd.yaml

@@ -125,7 +125,9 @@ jobs:
           CACHE_REF_WEB: git.shx.one/${{ steps.meta.outputs.owner_lc }}/evobgp-buildcache:web-buildcache
           CACHE_REF_BIRDC: git.shx.one/${{ steps.meta.outputs.owner_lc }}/evobgp-buildcache:birdc-buildcache
           BUILDX_BAKE_ENTITLEMENTS_FS: "0"
+          BUILDX_BAKE_FILE_RELATIVE_PATHS: "1"
           MIRROR_ENV_FILE: ${{ runner.temp }}/mirror-base.env
+        working-directory: deploy/docker
         run: |
           set -euxo pipefail
           if [ -f "${MIRROR_ENV_FILE}" ]; then
@@ -135,4 +137,4 @@ jobs:
             set +a
           fi
           docker buildx bake --allow=fs.read="${{ github.workspace }}" \
-            -f deploy/docker/docker-bake.hcl default --push
+            -f docker-bake.hcl default --push