Updates GitLab URL documentation

[fanny-jiang]

What does this PR do?

Update the gitlab documentation with correct instructions for specifying the gitlab url with authentication. Per the GitLab documentation, the token url format is supported for all tiers including EE and CE:

• https://docs.gitlab.com/ee/api/
• https://docs.gitlab.com/ee/api/#authentication

Motivation

Customer request

Additional Notes

Review checklist (to be filled by reviewers)

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] PR title must be written as a CHANGELOG entry (see why)
• [ ] Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• [ ] PR must have changelog/ and integration/ labels attached

[codecov[bot]]

Codecov Report

Merging #12683 (9baa8b6) into master (ab56491) will not change coverage. The diff coverage is n/a.

Flag	Coverage Δ
gitlab	89.94% <ø> (ø)

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