Extension Manager: Initial update fetch is slow

[0cyn]

Version and Platform (required):

• Binary Ninja Version: 5.4.9544

Bug Description:
Initial update fetch is slow as it requires making network requests to a large amount of URLs to pull version info for every single extension. Binary Ninja should only pull a extension's versions whenever a user clicks that extension.

Steps To Reproduce:
Run the app with a clean user directory and debug logging enabled and observe the time it takes for the Extension Manager to download the totality of remote plugins.
This will also occur whenever a new repository is added.

Expected Behavior:
The initial fetch should be near instant

[psifertex]

Re-opening this and moving to L. We have mitigated this significantly (performance is an order of magnitude better), but there are further optimizations we can do, specifically using a combined endpoint for latest updates instead of querying each plugin separately.