Clarify "support" to mean GitLab.com integration
What does this MR do?
Clarifies what is meant by "GitLab support" as a prerequisite for importing GitLab.com repositories to a self-managed GitLab instance
The term "GitLab support" is somewhat vague, and can be confused with GitLab Support as a feature of paid tiers.
MR updates documentation to note that GitLab.com integration needs to be enabled on the Gitlab instance instead of GitLab support.