RFR: 438: Add "git pr issue" subcommand [v2]

[Erik Helin]

> Hi all,
> 
> please review this patch that adds the `git pr issue` subcommand (corresponding
> to the `/issue` pull request command). A user can now run e.g. `git pr issue
> --add=SKARA-419` instead of the pull request command `/issue add SKARA-419`.
> 
> Testing:
> - [x] Manual testing of Linux x64
> 
> Thanks,
> Erik

Erik Helin has updated the pull request incrementally with one additional commit since the last revision:

  Use correct action
  
  Co-authored-by: Robin Westberg <robin at westberg.se>

-------------

Changes:
  - all: https://git.openjdk.java.net/skara/pull/684/files
  - new: https://git.openjdk.java.net/skara/pull/684/files/8ce3917e..d8f4b545

Webrevs:
 - full: https://webrevs.openjdk.java.net/skara/684/webrev.01
 - incr: https://webrevs.openjdk.java.net/skara/684/webrev.00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/684.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/684/head:pull/684

PR: https://git.openjdk.java.net/skara/pull/684