RFR: 2255: Keep additional issue marker updated

[Zhao Song]

Currently, additional issue marker is not updated automatically, it means if user changed the title of an additional issue in JBS, the user will need to issue `/issue` command again to update the additional issue. However, for additional issues, users are not aware that skara bot would store the issue title in a hidden marker.  To avoid confusion, we'd better let skara bot update the hidden marker automatically when user changes the issue title in JBS.

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Commit messages:
 - update
 - SKARA-2255

Changes: https://git.openjdk.org/skara/pull/1649/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1649&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2255
  Stats: 60 lines in 5 files changed: 51 ins; 4 del; 5 mod
  Patch: https://git.openjdk.org/skara/pull/1649.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1649/head:pull/1649

PR: https://git.openjdk.org/skara/pull/1649