feat: add the sync-ngrok command

[eberle1080]

This adds a new command, "sync-ngrok". It will wait for ngrok to be running, figure out what the public URL is, and update one or more Ampersand destinations to point to the ngrok URL (that is, it will swap out the domain - the path will be preserved).

I did this because I got tired of updating destinations by hand every time I had to re-run ngrok for local testing.

20250714194552124.mp4

[Copilot]

Pull Request Overview

Adds a hidden CLI command sync-ngrok that waits for a local ngrok instance, fetches its public URL, and updates specified Ampersand webhook destinations to use the ngrok tunnel.

• Introduces sync-ngrok subcommand with flags for destinations, ngrok server, protocol, and confirmation.
• Implements retry/backoff logic to wait for ngrok and fetch tunnel URLs (with interactive selection).
• Adds logic to merge ngrok URLs into existing webhook destinations and apply updates via the API.

Comments suppressed due to low confidence (1)

cmd/sync_ngrok.go:567

• [nitpick] The URL merging logic has several edge cases (paths, queries, fragments). Consider adding unit tests for mergeURLs to verify correct behavior across various input combinations.

func mergeURLs(ngrokURL, existingURL string) (string, error) {