Assign low priority to telemetry requests

[akhenry]

Is your feature request related to a problem? Please describe.
Telemetry requests that are slow to return can block the UI by preventing domain objects and static assets from loading. Open MCT has UI provision for slow telemetry requests, but not for a blocked UI.

Describe the solution you'd like
Specifying fetch priority is a non-guaranteed, but low risk option that should help the browser to prioritize requests appropriately, and may modestly alleviate contention for limited HTTP requests.

This has also been addressed on the Open MCT side.

[akhenry]

Also need to assignhigh priority to MDB requests.