Add ability to remove panels in analytics dashboard

What does this MR do and why?

Adds the ability to remove dashboard panels from analytics / customizable dashboards when in editing mode.

Note: Analytics dashboard is an experimental feature hidden behind a default off feature flag

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Follow these instructions to setup Product Analytics in GDK.
2. Onboard Product Analytics by setting up the feature at Project > Analytics > Analytics dashboards.
3. Enable custom dashboards by following the alert prompt on Project > Analytics > Analytics dashboards.
4. Create a new custom dashboard by clicking on New dashboard on Project > Analytics > Analytics dashboards.
5. Edit your newly created custom dashboard by clicking on Edit button, making some changes and clicking Save your dashboard.
6. Verify that panels can be removed during editing.

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.

Related to #410350 (closed)