tracking: opt-out of v1 requests on the directory

[arminsabouri]

Over the past couple months we noticed that only a small subset of payjoin sessions are v1. Directory operators should have the option to opt out of storing and forwarding plaintext requests (bip78).

• v2 reciever should be able to opt out of v1 senders #677
• config/feature flag v1 requests on the directory Gate V1 protocol behind runtime feature flag #1336
• The directory needs a way to declare its compatability with bip78. Otherwise clients would have to post a requests which could write to disk. Might need a new endpoint displaying the capabilities of the directory. Or a GET on the same endpoint to receieve the same information. Add supported versions to /health response #1348
• how to communicate this to intergrations if (payjo.in) decides to opt-out of supporting v1 requests.

[Mshehu5]

Would like to work on this if no one is woking on it