🌱 Consolidate GitLab e2e workflows.

[spencerschrock]

What kind of change does this PR introduce?

ci change, trying to reduce CI time

• PR title follows the guidelines defined in our pull request documentation

What is the current behavior?

• The gitlab e2e tests on PR runs in serial with the github e2e tests.
• The gitlab tests are defined in multiple places

What is the new behavior (if this is a feature change)?**

• The workflows are centralized in gitlab.yml.

• The gitlab e2e test runs in parallel with the github e2e tests.

• There's a few if statements to make sure the right commit gets checked out, and the right test run for the environment.

• Tests for the changes have been added (for bug fixes/features)

Which issue(s) this PR fixes

NONE

Special notes for your reviewer

I did test some of the fallback value semantics here and code checks out the right contents.

Does this PR introduce a user-facing change?

For user-facing changes, please add a concise, human-readable release note to
the release-note

(In particular, describe what changes users might need to make in their
application as a result of this pull request.)

[codecov]

Codecov Report

Merging #3278 (2a98621) into main (9f96ded) will decrease coverage by 6.45%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3278      +/-   ##
==========================================
- Coverage   72.18%   65.74%   -6.45%     
==========================================
  Files         173      173              
  Lines       12686    12686              
==========================================
- Hits         9158     8341     -817     
- Misses       3025     3877     +852     
+ Partials      503      468      -35