RFR: 1270: Allow different 'issues' urls for different repositories in mlbridge configuration

[Erik Joelsson]

The 'issues' URL in the mlbridge configuration is currently global for all repositories. We need to be able to configure different Jira instances for different repositories.

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Commit messages:
 - Repo specific issue tracker for mlbridge

Changes: https://git.openjdk.java.net/skara/pull/1254/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1254&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1270
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/1254.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1254/head:pull/1254

PR: https://git.openjdk.java.net/skara/pull/1254