feat: Checkly app connection and secrets sync (#4078)

* feat: checkly app connection
---------
Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

backend/src/services/app-connection/checkly/checkly-connection-fns.ts

@@ -0,0 +1,35 @@
+/* eslint-disable no-await-in-loop */
+import { AxiosError } from "axios";
+
+import { BadRequestError } from "@app/lib/errors";
+import { AppConnection } from "@app/services/app-connection/app-connection-enums";
+
+import { ChecklyConnectionMethod } from "./checkly-connection-constants";
+import { ChecklyPublicAPI } from "./checkly-connection-public-client";
+import { TChecklyConnectionConfig } from "./checkly-connection-types";
+
+export const getChecklyConnectionListItem = () => {
+  return {
+    name: "Checkly" as const,
+    app: AppConnection.Checkly as const,
+    methods: Object.values(ChecklyConnectionMethod)
+  };
+};
+
+export const validateChecklyConnectionCredentials = async (config: TChecklyConnectionConfig) => {
+  try {
+    await ChecklyPublicAPI.healthcheck(config);
+  } catch (error: unknown) {
+    if (error instanceof AxiosError) {
+      throw new BadRequestError({
+        message: `Failed to validate credentials: ${error.message || "Unknown error"}`
+      });
+    }
+
+    throw new BadRequestError({
+      message: "Unable to validate connection - verify credentials"
+    });
+  }
+
+  return config.credentials;
+};