Add add on name to duo pro lead/trial submissions

The following discussion from !168072 (merged) should be addressed:

• @dstull started a discussion:

  note (non-blocking):

  Even though CDOT currently defaults to code_suggestions for duo_pro case... we should probably do a follow-up to be more explicit on GitLab side for duo pro too and remove CDOT need for a default.

• Remove the default from CDOT once implemented and rolled out on GitLab.com

Implementation steps

1. deploy changes for gitlab to always pass the add-on name.
2. monitor all requests to CDot to ensure that all requests include that parameter.
3. deploy changes to CDot to avoid the default and log if it is not present.