Add `.firebaserc` and `firebaseConfigs.ts` to `.gitignore`

[ijemmao]

Is your feature request related to a problem? Please describe.
.firebaserc and firebaseConfigs.ts need to be updated by open source contributors to make changes to the repo. However, it's common that contributors forget to revert changes to these files when committing, which can lead to changes to our Firebase projects in production. This will cause issues in production. This is also a negative developer experience since contributors must remember not to break production with this specific change.

Describe the solution you'd like
Add .firebaserc and firebaseConfigs.ts to .gitignore

Describe alternatives you've considered
N/A

Additional context
N/A