Upgrade Patreon Discourse Plugin to API v2

[Falco]

@noertap

You can now create the v2 api client at Platform | Applications | Patreon

I can’t get this form to enable the submit button no matter what I try

Same thing that was reported at

Create Client button stays disabled even with all fields filled

It is the only blocker for me to merge the change

https://github.com/discourse/discourse/pull/38871