RFR: 1937: Re-evaulate all PRs when .jcheck/conf changes [v3]

[Zhao Song]

> As Erik said in the issue: "When we bump the version in .jcheck/conf from N to N+1 in the jdk master branch, PRs with CSRs are often not updated to reflect this."
> 
> This root cause of this is that changing of .jcheck/conf in target ref of the pr will not be able to trigger checkWorkItem for this pr.
> 
> In this patch,
> 1. The prBot will monitor the changes to the .jcheck/conf file in any branch(except for PR branches).
> 2. If the prBot detects an update to the .jcheck/conf file in a branch, it will trigger a checkWorkItem for all open PRs whose target ref is the branch where the .jcheck/conf file was updated.
> 3. To solve the problem related with bot restarting, the contents of the .jcheck/conf file in the target branch of a PR will be included in the metadata hash.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  Update forge/src/main/java/org/openjdk/skara/forge/HostedRepository.java
  
  Co-authored-by: Erik Joelsson <37597443+erikj79 at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.org/skara/pull/1531/files
  - new: https://git.openjdk.org/skara/pull/1531/files/89ff415f..81b96727

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1531&range=02
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1531&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1531.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1531/head:pull/1531

PR: https://git.openjdk.org/skara/pull/1531