Enable DHT and PEX for all repositories

[jnny]

Currently the instructions state that DHT and PEX need to be manually enabled per repository. It would be ideal to have an option to enable DHT and PEX peer discovery for all repositories (or at least all mounted repositories).

Not sure whether to label this as a bug or a feature.

[IvanaBlzvc]

https://redmine.equalit.ie/issues/31610