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/defs/static_source.go

@@ -23,7 +23,8 @@ type StaticSourceParent interface {
 
 // StaticSourceRunParams is the set of params passed to Run().
 type StaticSourceRunParams struct {
-	Context    context.Context
-	Conf       *conf.Path
-	ReloadConf chan *conf.Path
+	Context        context.Context
+	ResolvedSource string
+	Conf           *conf.Path
+	ReloadConf     chan *conf.Path
 }