RFR: 1118: The Skara PR bot should not block on a CSR if not enabled for a repo

[Guoxiong Li]

Hi all,

This patch adds a config item `enable-csr` for the PullRequestbot and then the `CSRCommand` firstly checks whether the csr is enabled. If not enabled, the `CSRCommand` will reply a message about it.

Thanks for taking the time to review.

Best Regards,
-- Guoxion

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Commit messages:
 - 1118: The Skara PR bot should not block on a CSR if not enabled for a repo

Changes: https://git.openjdk.java.net/skara/pull/1308/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1308&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1118
  Stats: 69 lines in 5 files changed: 62 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/skara/pull/1308.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1308/head:pull/1308

PR: https://git.openjdk.java.net/skara/pull/1308