Chore: Refactor API Swagger definitions and remove unused structs

- Removed deprecated `thumbnailParams` struct from `thumbnails.go`.
- Updated `server_test.go` to use an anonymous struct for response unmarshalling.
- Enhanced `swagger.json` with detailed definitions for SendRequest and SendMessageResponse.
- Introduced new `swaggerParams.go` to define Swagger parameters for various API endpoints.
- Created `swaggerResponses.go` to define Swagger responses for API endpoints.
- Cleaned up unused JSON error message definitions and consolidated error responses.
- Improved documentation for Chaos triggers and web UI configuration responses.

server/apiv1/api.go

@@ -35,9 +35,7 @@ func httpJSONError(w http.ResponseWriter, msg string) {
 	w.Header().Set("Referrer-Policy", "no-referrer")
 	w.Header().Set("Content-Security-Policy", config.ContentSecurityPolicy)
 	w.WriteHeader(http.StatusBadRequest)
-	e := JSONErrorMessage{
-		Error: msg,
-	}
+	e := struct{ Error string }{Error: msg}
 
 	w.Header().Add("Content-Type", "application/json")
 	if err := json.NewEncoder(w).Encode(e); err != nil {