Implement Prohibited Caches for Federation Prefixes

[Saartank]

This PR implements a step towards enabling users to configure a list of caches where data should not propagate for a given federation prefix.

Changes Introduced:

1. Modify Registry Database:

   • Added a new column, prohibited_caches, in the namespace table to store prohibited caches for federation prefixes. This column stores a list of prohibited cache hostnames.

2. Adjust Registry Endpoints:

   • Created a new endpoint: GET /api/v1.0/registry/namespaces/prohibitedCaches that returns a map of federation prefixes to their corresponding list of prohibited cache hostnames.
   • Modified existing registry and registry_ui namespace endpoints to include prohibited caches data in their responses.

3. Add Goroutine in Director:

   • Added a new goroutine in the director that periodically makes requests to the registry endpoint and maintains the director’s knowledge of prohibited caches in memory.
   • Added a new configuration parameter, Director.ProhibitedCachesRefreshInterval, to control the time interval at which this goroutine sends requests to the registry endpoint.

4. Update Matchmaking Logic:

   • Updated the director matchmaking logic to respect the configured prohibited caches.

[Saartank]

There have been major design changes requested for this task, and it will now be completed as part of a different PR altogether.