RFR: forge: add commitMetadata method to HostedRepository

[Erik Helin]

Hi all,

please review this patch that adds the method `CommitMetadata HostedRepository.commitMetadata(Hash h)`. This is useful
for getting the metadata for a commit from a `HostedRepository` instance without having to clone it first to a local
repository.

Testing:
- [ ] not in this commit, will be part of follow-up patches

Thanks,
Erik

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

Commit messages:
 - forge: add commitMetadata method to HostedRepository

Changes: https://git.openjdk.java.net/skara/pull/642/files
 Webrev: https://webrevs.openjdk.java.net/skara/642/webrev.00
  Stats: 66 lines in 6 files changed: 66 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/642.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/642/head:pull/642

PR: https://git.openjdk.java.net/skara/pull/642