Add project dropdown filter as a configurable dashboard filter

Background

The project dropdown filter is a common feature of many of our existing group-level dashboards (e.g. https://gitlab.com/groups/gitlab-org/-/analytics/productivity_analytics), its a common component used throughout the product to provide flexibility and a level of customization for users.

We should add support for a dashboard level filter bar

Requirements

• Can be enabled / disabled on a per dashboard level
• It's only available to group-level dashboards
• Persist filter selections in the URL: will do this separately #520212 (closed)