Add spectral linter for Swagger (#20321)

[spectral](https://github.com/stoplightio/spectral) lints
openapi/swagger files for mistakes of which it has identified a few and
which I've fixed.

I had to put it into `lint-frontend` because it depends on node_modules
so can not run on Drone during the backend target. I plan to refactor
these targets later to `lint-js` and `lint-go` so that they are
categorized based on the tool dependencies.

routers/api/v1/org/hook.go

@@ -100,7 +100,7 @@ func GetHook(ctx *context.APIContext) {
 
 // CreateHook create a hook for an organization
 func CreateHook(ctx *context.APIContext) {
-	// swagger:operation POST /orgs/{org}/hooks/ organization orgCreateHook
+	// swagger:operation POST /orgs/{org}/hooks organization orgCreateHook
 	// ---
 	// summary: Create a hook
 	// consumes:

routers/api/v1/swagger/options.go

@@ -107,9 +107,6 @@ type swaggerParameterBodies struct {
 	// in:body
 	EditUserOption api.EditUserOption
 
-	// in:body
-	MigrateRepoForm forms.MigrateRepoForm
-
 	// in:body
 	EditAttachmentOptions api.EditAttachmentOptions