Add group-accessible-repos option (#308)

* Add group-accessible-repos option

The group-accessible-repos option will let filesystem group id
be able to access files and dir within the restic repo
Default stick with old behaviour to be owner restricted
While here make dirMode and fileMode within Options struct
private

---------

Co-authored-by: Michael Eischer <michael.eischer@fau.de>

handlers.go

@@ -15,23 +15,24 @@ import (
 
 // Server encapsulates the rest-server's settings and repo management logic
 type Server struct {
-	Path             string
-	HtpasswdPath     string
-	Listen           string
-	Log              string
-	CPUProfile       string
-	TLSKey           string
-	TLSCert          string
-	TLS              bool
-	NoAuth           bool
-	AppendOnly       bool
-	PrivateRepos     bool
-	Prometheus       bool
-	PrometheusNoAuth bool
-	Debug            bool
-	MaxRepoSize      int64
-	PanicOnError     bool
-	NoVerifyUpload   bool
+	Path                 string
+	HtpasswdPath         string
+	Listen               string
+	Log                  string
+	CPUProfile           string
+	TLSKey               string
+	TLSCert              string
+	TLS                  bool
+	NoAuth               bool
+	AppendOnly           bool
+	PrivateRepos         bool
+	Prometheus           bool
+	PrometheusNoAuth     bool
+	Debug                bool
+	MaxRepoSize          int64
+	PanicOnError         bool
+	NoVerifyUpload       bool
+	GroupAccessibleRepos bool
 
 	htpasswdFile *HtpasswdFile
 	quotaManager *quota.Manager
@@ -88,12 +89,13 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	// Pass the request to the repo.Handler
 	opt := repo.Options{
-		AppendOnly:     s.AppendOnly,
-		Debug:          s.Debug,
-		QuotaManager:   s.quotaManager, // may be nil
-		PanicOnError:   s.PanicOnError,
-		NoVerifyUpload: s.NoVerifyUpload,
-		FsyncWarning:   &s.fsyncWarning,
+		AppendOnly:      s.AppendOnly,
+		Debug:           s.Debug,
+		QuotaManager:    s.quotaManager, // may be nil
+		PanicOnError:    s.PanicOnError,
+		NoVerifyUpload:  s.NoVerifyUpload,
+		FsyncWarning:    &s.fsyncWarning,
+		GroupAccessible: s.GroupAccessibleRepos,
 	}
 	if s.Prometheus {
 		opt.BlobMetricFunc = makeBlobMetricFunc(username, folderPath)