fix: prevent panic on invalid regex in reload annotation

ShouldReload compiled each comma-separated value of a named reload
annotation (e.g. secret.reloader.stakater.com/reload) with
regexp.MustCompile, which panics on an invalid pattern. The value comes
straight from a user-set annotation on a watched workload, and the queue
worker has no recover(), so a single malformed annotation (e.g.
"app-config[") on any workload in any watched namespace crashes Reloader
and stops reloads cluster-wide.

Use regexp.Compile and, on error, log and skip that pattern instead of
panicking.

pkg/common/common.go

@@ -276,7 +276,11 @@ func ShouldReload(config Config, resourceType string, annotations Map, podAnnota
 	values := strings.Split(annotationValue, ",")
 	for _, value := range values {
 		value = strings.TrimSpace(value)
-		re := regexp.MustCompile("^" + value + "$")
+		re, err := regexp.Compile("^" + value + "$")
+		if err != nil {
+			logrus.Errorf("Invalid regex %q in reload annotation %q on resource '%s' of type '%s'; skipping this pattern: %v", value, config.Annotation, config.ResourceName, config.Type, err)
+			continue
+		}
 		if re.Match([]byte(config.ResourceName)) {
 			return ReloadCheckResult{
 				ShouldReload: true,