reload service registration configuration on SIGHUP (#17598)

* add reloading service configuration

* add changelog entry

* add tests

* fix typo

* check if config.ServiceRegistration is nil before signaling

* add changes for deregistering service on nil config with failing tests

* fix tests by decreasing reconcile_timeout + setting consul agent tokens

* fix races

* add comments in test

---------

Co-authored-by: Marc Boudreau <marc.boudreau@hashicorp.com>

command/server.go

@@ -1685,6 +1685,15 @@ func (c *ServerCommand) Run(args []string) int {
 				}
 			}
 
+			// notify ServiceRegistration that a configuration reload has occurred
+			if sr := coreConfig.GetServiceRegistration(); sr != nil {
+				var srConfig *map[string]string
+				if config.ServiceRegistration != nil {
+					srConfig = &config.ServiceRegistration.Config
+				}
+				sr.NotifyConfigurationReload(srConfig)
+			}
+
 			if err := core.ReloadCensus(); err != nil {
 				c.UI.Error(err.Error())
 			}