[skara] RFR: forge: add HostedRepository.createPullRequestUrl [v2]

[Erik Helin]

> Hi all,
> 
> please review this small patch that adds the `HostedRepository.createPullRequestUrl` for getting the URL that a user can click to create a pull request between two `HostedRepository` instances.
> 
> Thanks,
> Erik

Erik Helin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase.

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Changes:
  - all: https://git.openjdk.java.net/skara/pull/1028/files
  - new: https://git.openjdk.java.net/skara/pull/1028/files/dcbc2c19..dcbc2c19

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=1028&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=1028&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/1028.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1028/head:pull/1028

PR: https://git.openjdk.java.net/skara/pull/1028