If the New Code Period is configured to use a branch as a reference, the scanner should use the SCM to find the merge base between the branch being analyzed and the reference branch.
This ticket involves the following changes:
- A new method in the SCM plugin API so that the plugins can provide this information.
- Scanner needs to access api/newcodeperiod/show to check the configuration for the branch being analyzed.
- The scanner report needs a new field for the date