onedrive: allow setting permissions to fail if failok flag is set

For example using

    --onedrive-metadata-permissions read,write,failok

Will allow permissions to be read and written but if the writing
fails, then only an ERROR will be written in the log and the transfer
won't fail.

backend/onedrive/metadata.go

@@ -133,6 +133,7 @@ func (rwChoices) Choices() []fs.BitsChoicesInfo {
 		{Bit: uint64(rwOff), Name: "off"},
 		{Bit: uint64(rwRead), Name: "read"},
 		{Bit: uint64(rwWrite), Name: "write"},
+		{Bit: uint64(rwFailOK), Name: "failok"},
 	}
 }
 
@@ -142,6 +143,7 @@ type rwChoice = fs.Bits[rwChoices]
 const (
 	rwRead rwChoice = 1 << iota
 	rwWrite
+	rwFailOK
 	rwOff rwChoice = 0
 )
 
@@ -158,6 +160,9 @@ var rwExamples = fs.OptionExamples{{
 }, {
 	Value: (rwRead | rwWrite).String(),
 	Help:  "Read and Write the value.",
+}, {
+	Value: rwFailOK.String(),
+	Help:  "If writing fails log errors only, don't fail the transfer",
 }}
 
 // Metadata describes metadata properties shared by both Objects and Directories
@@ -363,6 +368,15 @@ func (m *Metadata) WritePermissions(ctx context.Context) (err error) {
 	if m.normalizedID == "" {
 		return errors.New("internal error: normalizedID is missing")
 	}
+	if m.fs.opt.MetadataPermissions.IsSet(rwFailOK) {
+		// If failok is set, allow the permissions setting to fail and only log an ERROR
+		defer func() {
+			if err != nil {
+				fs.Errorf(m.fs, "Ignoring error as failok is set: %v", err)
+				err = nil
+			}
+		}()
+	}
 
 	// compare current to queued and sort into add/update/remove queues
 	add, update, remove := m.sortPermissions()