Add GitLab Cloud and GitLab Self-Hosted to Enterprise Integrations page

Summary

Update the Enterprise Integrations page to clearly specify which GitLab variants are supported on OHE vs SaaS/Cloud.

Current State

The page currently says:

Source Control: GitHub Enterprise, GitLab, and Bitbucket Data Center

This is ambiguous about:

• Whether "GitLab" means gitlab.com (cloud) or self-hosted
• Which variants are supported on which product (OHE vs SaaS)

Requested Changes

Clarify the text to be:

Source Control: GitHub Enterprise, GitLab (gitlab.com), GitLab Self-Hosted, and Bitbucket Data Center

Context

Internally, GitLab Self-Hosted is supported on OHE (not SaaS/Cloud). We should make this clearer in the docs to avoid prospect confusion.

Acceptance Criteria

• Update integration list to explicitly mention both GitLab cloud and self-hosted variants
• Consider adding a note or table clarifying which integrations are supported on which product (OHE vs SaaS/Cloud)

References

• Slack discussion confirming GitLab Self-Hosted is OHE-only
• https://docs.openhands.dev/enterprise

Open the Enterprise Integrations page linked in the issue and find the current Source Control integration list. Update it to name GitLab (gitlab.com) and GitLab Self-Hosted, then verify the rendered page clearly communicates the relevant OHE and SaaS/Cloud support distinctions described in the issue.