feat(api): Configurable response time badge thresholds (#309)

* recreated all changes for setting thresholds on Uptime Badges

* Suggestion accepted: Update core/ui/ui.go

Co-authored-by: TwiN <twin@linux.com>

* Suggestion accepted: Update core/ui/ui.go

Co-authored-by: TwiN <twin@linux.com>

* implemented final suggestions by Twin

* Update controller/handler/badge.go

* Update README.md

* test: added the suggestons to set the UiConfig at another line

Co-authored-by: TwiN <twin@linux.com>

core/endpoint.go

@@ -145,6 +145,10 @@ func (endpoint *Endpoint) ValidateAndSetDefaults() error {
 	}
 	if endpoint.UIConfig == nil {
 		endpoint.UIConfig = ui.GetDefaultConfig()
+	} else {
+		if err := endpoint.UIConfig.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
 	}
 	if endpoint.Interval == 0 {
 		endpoint.Interval = 1 * time.Minute