[STAL-2949] Make git author a mandatory field

[dastrong]

What and why?

We use an author email to implement billing and thus it should be a required field.

How?

Adds the git author email tag to the mandatory fields object.

Review checklist

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration)

[datadog-datadog-prod-us1[bot]]

Datadog Report

Branch report: dastrong/STAL-2949 Commit report: 9827787 Test service: datadog-ci-tests

:white_check_mark: 0 Failed, 6184 Passed, 0 Skipped, 2m 50.46s Total duration (43.56s time saved)