feat(store): introduce GitTokenStore for token persistence via Git backend

- Added `GitTokenStore` to handle token storage and metadata using Git as a backing storage.
- Implemented methods for initialization, save, retrieval, listing, and deletion of auth files.
- Updated `go.mod` and `go.sum` to include new dependencies for Git integration.
- Integrated support for Git-backed configuration via `GitTokenStore`.
- Updated server logic to clone, initialize, and manage configurations from Git repositories.
- Added helper functions for verifying and synchronizing configuration files.
- Improved error handling and contextual logging for Git operations.
- Modified Dockerfile to include `config.example.yaml` for initial setup.
- Added `gitCommitter` interface to handle Git-based commit and push operations.
- Configured `Watcher` to detect and leverage Git-backed token stores.
- Implemented `commitConfigAsync` and `commitAuthAsync` methods for asynchronous change synchronization.
- Enhanced `GitTokenStore` with `CommitPaths` method to support selective file commits.

internal/misc/copy-example-config.go

@@ -0,0 +1,40 @@
+package misc
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+
+	log "github.com/sirupsen/logrus"
+)
+
+func CopyConfigTemplate(src, dst string) error {
+	in, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if errClose := in.Close(); errClose != nil {
+			log.WithError(errClose).Warn("failed to close source config file")
+		}
+	}()
+
+	if err = os.MkdirAll(filepath.Dir(dst), 0o700); err != nil {
+		return err
+	}
+
+	out, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if errClose := out.Close(); errClose != nil {
+			log.WithError(errClose).Warn("failed to close destination config file")
+		}
+	}()
+
+	if _, err = io.Copy(out, in); err != nil {
+		return err
+	}
+	return out.Sync()
+}