Save Custom Dashboards to other Repo in dashboard Designer

What does this MR do and why?

Resolves the issue #370626 (closed) (find more information there)

• Makes it possible to save changed custom dashboards to the configured repo through the commit API
• Adds a title box when activating editing mode to change the dashboard name
• Doesn't show a save button for predefined GitLab dashboards that come with the product
• Adds GitLab labels to our predefined dashboards for easier visual differentiation

Screenshots or screen recordings

How to set up and validate locally

1. Make sure you are on GitLab Ultimate
2. You need to set up the Product Analytics DevKit if you haven't already done so. And follow the instructions on Connecting GDK to your devkit.
3. Configure a custom dashboard project like in !112481 (merged)
4. Access /-/analytics/dashboards/ on an product analytics activated project like [GDK_HOST]/gitlab-org/gitlab-shell/-/analytics/dashboards/.
5. Click Edit move Panels and hit save, which then will save it to the other repository

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

closes #370626 (closed)