Send an email notification when an application is connected through OAuth

[Betree]

Moved from @hdiniz's fork (https://github.com/opencollective/opencollective-api/pull/7737) to our main repo Resolves https://github.com/opencollective/opencollective/issues/5614

Email for new oauth application authorized

Email for new oauth application authorized with scopes

There is a refactor of the notifications flow on https://github.com/opencollective/opencollective-api/pull/7713 close to being merged, when that happens I will rebase this change.