Provide RegEx fields correlated with each e-mail field, for plus addresses.

Is your feature request related to a problem? Please describe.

I utilise an obfuscator for all of my e-mail addresses. ^1 Because it offers infinite aliases, I use a different alias every time I give my e-mail address to someone. However, I ensure that they're all under the @rokejulianlockhart.addy.io domain, so that they can be identified as me by a human. However, this isn't good enough. I use different aliases to combat spam, not be anonymous.

Additionally, when messaging others, I ensure that I add an RFC 5233-compliant sub-address with my name to their e-mail address, ^2 so that they can filter all messages from me (even if I'm using a different alias for my own filtering purposes). Others use the same when communicating with me, especially family. The current identification system doesn't take sub addresses into account whatsoever.

Describe the solution you'd like

I should, therefore, be able to set RY7I0I+RY7I0R@beedellRoke.addy.IO as an e-mail address, and, beneath it, add, for instance, the undermentioned:

[A-Za-z0-9]+\+[A-Za-z0-9]+@beedellRoke\.Addy\.IO

…in another input form to ensure that Nextcloud identifies any (in this case sub-addressed) alias as me.

Describe alternatives you've considered

The sole current alternative is to list literal tens of thousands of aliases as myself, which is insane:

It also wouldn't work, because the service generates a new alias when someone else uses one, so I'd have to retroactively add those whenever someone else uses one. It also wouldn't account for sub-addresses.

Additional context

Like most more powerful features of Nextcloud, this only need be visible when clicked on. Adding a button beside each e-mail address to show a form which allows the user to enter custom regex is enough.

Additionally requested at:

1. feedbackportal.microsoft.com/feedback/idea/ed4261f8-af28-ee11-a81c-6045bd8534ad

2. discussions.apple.com/thread/255016441

3. developer.apple.com/forums/thread/734290

4. bugzilla.mozilla.org/show_bug.cgi?id=1845009#c0

The issue names no files, tests, or entry points. Start by tracing how Contacts currently identifies matching e-mail addresses and how each e-mail field is stored and edited; the work is done when a user can configure a regex for an address and matching plus-addressed aliases are recognized without listing them individually.