API: Enable serving Swagger UI by default and add docs and guidelines (#63489)

* Enable serving Swagger UI by default

It used to be served behind the `swaggerUi` feature toggle.

* Remove `swaggerUi` feature toggle

* Add docs and guidelines for updating swagger

* Apply suggestions from code review

Co-authored-by: Josh Hunt <joshhunt@users.noreply.github.com>

pkg/services/featuremgmt/registry.go

@@ -83,11 +83,6 @@ var (
 			Description: "Use experimental loki api for WebSocket streaming (early prototype)",
 			State:       FeatureStateAlpha,
 		},
-		{
-			Name:        "swaggerUi",
-			Description: "Serves swagger UI",
-			State:       FeatureStateBeta,
-		},
 		{
 			Name:        "featureHighlights",
 			Description: "Highlight Grafana Enterprise features",

pkg/services/featuremgmt/toggles_gen.go

@@ -63,10 +63,6 @@ const (
 	// Use experimental loki api for WebSocket streaming (early prototype)
 	FlagLokiDataframeApi = "lokiDataframeApi"
 
-	// FlagSwaggerUi
-	// Serves swagger UI
-	FlagSwaggerUi = "swaggerUi"
-
 	// FlagFeatureHighlights
 	// Highlight Grafana Enterprise features
 	FlagFeatureHighlights = "featureHighlights"