Update Chart.yaml

What does this MR do?

I just noticed that the description of the GitLab Helm chart does not really describe GitLab.

Current description:

Web-based Git-repository manager with wiki and issue-tracking features.

I would prefer to emphasize the single application for the whole DevSecOps lifecycle aspect of GitLab.

Related issues

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened