[skara] RFR: pr: add /integrate auto

[Erik Helin]

Hi all,

please review this patch that adds the `auto` and `manual` arguments to the `/integrate` pull request command. If a contributor issues `/integrate auto` then the pull request will be automatically integrated when the pull request is ready (i.e. when jcheck passes). To aid reviewers that this is the case the label "auto" will be added to such pull requests. A contributor can always go back to "manual" mode by issuing the `/integrate auto`.

This functionality is useful for smaller patches where you are certain that they are correct, for example fixing a typo in a comment. It it also useful for clean backports since most projects consider clean backports ready to be integrated without a review. This allows a backporter to add `/integrate auto` to the bottom of the PR body for a clean backport and then it will automatically be integrated if it is considered clean.

I also added a bunch of unit tests.

Thanks,
Erik

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Commit messages:
 - pr: add /integrate auto

Changes: https://git.openjdk.java.net/skara/pull/1071/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1071&range=00
  Stats: 403 lines in 6 files changed: 389 ins; 6 del; 8 mod
  Patch: https://git.openjdk.java.net/skara/pull/1071.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1071/head:pull/1071

PR: https://git.openjdk.java.net/skara/pull/1071