Change `gitlab` and `gitlab-runner` charts to be vendored

What does this MR do?

Part of gitlab-com/gl-infra/delivery#1982 (closed)

This change moves the last two charts we use in this repo (gitlab and gitlab-runner) to be vendored completely in this repository. This is accomplished by using tooling vendor-chart.sh to automate the vendoring and commiting it to the current branch.

This change also includes updated information in the README.md on how to specify the chart we are using in each environment (pre, gstg, gprd. Unfortunately cny stage is not supported yet).

This means this repository is now completely self-contained, with no extra callouts during execution time. Because of this, I have dropped the build-artifact job from CI.

Author Check-list

Please read the Contributing document and once you do, complete the following:

• Assign to the correct reviewer per the contributing document
• Apply the correct metadata per the contributing document
• Link to related MRs for applying the changes on other environments
• Link to related Chef changes
• If necessary link to a Criticality 4 Change Request issue

Reviewer Check-list

• Reviewed the diff jobs to confirm changes are as expected
• No changes shown in the diffs not associated with this MR - This may require a rebase or further investigation