Allow custom regex patterns for linking external issues

[tgdchmi2]

• Gitea version (or commit ref): 1.3.2
• Git version: 2.16.1
• Operating system: Linux
• Database (use [x]):
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  • MySQL
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  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
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  • No
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• Log gist:

Description

For external issue tracker: alphanumeric issue recognition does not work when:

• Key before the dash contains a number. Example: BLG5-456
• Key is enclosed in quotes. Example: 'BLG-456' or "BLG-456"
• Key follows a slash: Example BLG-123/BLG-564 (first key is recognized, second one not)

We think implementing so many additional 'rules' could lead to many false positives.
Thus we propose to add a third External Issue Tracker Naming Style for specifying custom patterns to apply for matching issue keys. Then we could specify a pattern like (WP-\d+)|(BLG5-\d+) ourselves.
The matched group should then be used for replacing {index} in the External Issue Tracker URL Format.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.

[strk]

See also #7084 for an even more flexible mapping idea

[jonny64]

Hi, we have tasks/{uuid v4} as issue {index}, what should we do?