allow using MTX_QUERY inside source (#3486)

this allows to pass query parameters to sources, for instance:

source: rtsp://my_host/my_path?$MTX_QUERY
sourceOnDemand: true

internal/staticsources/rtsp/source.go

@@ -62,7 +62,6 @@ func createRangeHeader(cnf *conf.Path) (*headers.Range, error) {
 
 // Source is a RTSP static source.
 type Source struct {
-	ResolvedSource string
 	ReadTimeout    conf.StringDuration
 	WriteTimeout   conf.StringDuration
 	WriteQueueSize int
@@ -104,7 +103,7 @@ func (s *Source) Run(params defs.StaticSourceRunParams) error {
 		},
 	}
 
-	u, err := base.ParseURL(s.ResolvedSource)
+	u, err := base.ParseURL(params.ResolvedSource)
 	if err != nil {
 		return err
 	}