feat: add metrics for repository migration status

Adds a gauge to track migration status.

changes are treated like transactions (eg. PreImportInProgress -> PreImportComplete) so that there is always have a reliable snapshot of the active repositories.

Note: repositories with import status RepositoryStatusNative are not tracked.

Closes #512 (closed)

registry/handlers/internal/metrics/metrics.go

@@ -158,9 +158,9 @@ func ImportWorkerSaturation(percentage float64) {
 	concurrentImports.Set(percentage)
 }
 
-func MigrationStatus(from migration.RepositoryStatus, to migration.RepositoryStatus) {
-	if from != migration.RepositoryStatusNative {
-		importMigrationStatus.WithLabelValues(string(from)).Dec()
+func MigrationStatus(from string, to string) {
+	if from != "" {
+		importMigrationStatus.WithLabelValues(from).Dec()
 	}
-	importMigrationStatus.WithLabelValues(string(to)).Inc()
+	importMigrationStatus.WithLabelValues(to).Inc()
 }