Support both numeric and alphanumeric External Issue Tracker Number Format

[strk]

Feature Description

We recently decided to move to a new issue tracker but the git repository is full of numeric issue tracker numbers, like #1012.
In order to distinguish, in history, between the old tracker and the new tracker, we plan to use NT-10 syntax but the current repository settings for Gitea only allows either Numeric or Alphanumeric, not both, so if we enable Alphanumeric the #1012references will stop working.

I do like the fact that when Alphanumeric is enabled the external tracker also receives the alphabetic part of the reference (so it can redirect the user to the appropriate tracker) but unless the #1012 old references turn to links, we're missing links from the historical tracker.

This issue is to allow rendering both syntaxes, passing the whole information to the external tracker.

Screenshots

No response

[lunny]

Looks like complicated.

[strk]

Isn't #4265 going in that direction ?