RFR: 1071: auto-set `/csr` flag from JBS state

[Guoxiong Li]

Hi all,

Currently, the author of the PR or a reviewer could type `/csr` in the comment to direct the need of the CSR.
It is good for the bot to automatically scan the `scr for` link and set the `csr` label for the PR.

This patch adds the automatically scanning feature. And the corresponding tests are added.

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - 1071: auto-set /csr flag from JBS state

Changes: https://git.openjdk.java.net/skara/pull/1245/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1245&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1071
  Stats: 169 lines in 6 files changed: 145 ins; 13 del; 11 mod
  Patch: https://git.openjdk.java.net/skara/pull/1245.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1245/head:pull/1245

PR: https://git.openjdk.java.net/skara/pull/1245