Create new customizable dashboards packages rule

Adding a rule to allow customizable dashboards packages to be automatically version bumped and reviewed by groupproduct analytics team members. Customizable dashboards is a shared feature, so other groups may also begin contributing to this feature, which is why I've separated it from the product analytics specific rule. For now though, groupproduct analytics are the DRI.

This rule will assign @rob.hunt, @jiaan, @elwyn-gitlab to any customizable dashboards specific package version bumps. We currently make use of one package:

Package name	Used for	Initially introduced
@gridstack	Used to render an orderable, resizeable, modifiable grid	First version for editing Dashboards (gitlab-org/gitlab!107966 - merged)

Related to gitlab-org/gitlab#383702 (closed) in the sense that we released there was another package we should monitor 😅