Add GH Action to warn devs about sentryAuthToken changes

[krystofwoldrich]

Description

To prevent GHSA-68c2-4mpx-qh95 in the future, we can add a GitHub Action which will add a warning to a PR when changes related to handling sentry auth token are included.

Impl can be a simple string search for sentryAuthToken, SENTRY_AUTH_TOKEN, and similar.

[krystofwoldrich]

This warning should not be triggered for changes in GH actions yml files.

[lucas-zimerman]

This may be closed once getsentry/.github#134 is fixed

[krystofwoldrich]

This GH Issue is about adding a warning like getsentry/sentry-cocoa#4091 (comment)

For example changes in https://github.com/getsentry/sentry-react-native/blob/9d86532d68474e40b8d0c346799236ab466c0cb7/plugin/src/withSentry.ts related to the authToken variable should trigger such a warning.