Add git credentials to .netrc when needed

What does this MR do?

Avoid having to remember to call try_add_credentials_to_netrc after setting credentials.

There is an EE MR to make sure the EE tests pass: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9322 - it shouldn't need to be merged

What are the relevant issue numbers?

• Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56857
• Closes https://gitlab.com/gitlab-org/quality/nightly/issues/57

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• [-] Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer