Rename `app-id` input to `client-id` or `app-client-id`

[gr2m]

As discussed at #136 (comment) we probably want to eventually replace app-id with client-id or app-client-id in order to align with GitHub's recommendation to use the app's client ID instead of app ID for authentication.

[github-actions]

This issue has been marked stale because it has been open for 180 days with no activity. Please close this issue if it is no longer needed. If this issue is still relevant and you would like it to remain open, simply update it within the next 60 days.

[jeffwidman]

@parkerbxyz I just noticed the 3.x release was cut, too bad this wasn't included... can you re-open and remove the stale flag? Probably make this a v4 breaking changes issue...