Bring back main programming language in repo

Description

We removed the main language feature on 8.9 due to a preformance issue, but it would be great if we could re visit this.

Proposal

Improve performance on main language feature and add it again.

Links / references

• https://gitlab.com/gitlab-org/gitlab-ce/commit/85495c8c85533e2d4156231fd2535270afffef5a/
• ZD: https://gitlab.zendesk.com/agent/tickets/45721

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/cc @twk3