Hook to filter list of e-mails

[espellcaste]

Suggestion: Allow devs to hook into the bp_email_get_schema so that they can add or remove emails.

One can add emails via the bp_core_install_emails hook, but it is not that easy to remove it. Forcing the developer to come up with creative ways to accomplish this task.

Also, a lot of code is duplicated in the bp_core_install_emails function to create new emails. So the hook on the schema function would avoid this code duplication.

[espellcaste]

I'm claiming this one!

[imath]

I believe we should add unit tests to make sure we don't break anything ;)

[espellcaste]

It is unlikely this hook will break something. It is just to make easier for adding custom emails.

[imath]

Ok, looks good 👌

[espellcaste]

In 12691:

On bp_email_get_schema, we are adding a bp_email_get_schema hook to facilitate the addition and removal of BuddyPress emails.

Props imath

Fixes #8173