RFR: 1852: Make it possible to disable backport PRs for repository [v3]

[Zhao Song]

> In this patch, PR bot has been added with the capability to control whether backport pr is allowed in specific repositories.
> 
> By default, backport is enabled.
> 
> However, if it is desired to disable backport in a repo, the configuration can be added to the PR bot configuration as follows:
> 
> {
>   "pr": {
>       "repositories": {
>           "repo1": {
>                "backport": false
>           }
>        }
>   }
> }
> 
> 
> If backport pr is disabled and the title of the pr matches the pattern of backport pr, the pr bot would reply a warning message to the user and prompt for the next steps.

Zhao Song has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:

 - Merge branch 'master' into SKARA-1852
   
   # Conflicts:
   #	bots/pr/src/main/java/org/openjdk/skara/bots/pr/PullRequestBot.java
   #	bots/pr/src/main/java/org/openjdk/skara/bots/pr/PullRequestBotBuilder.java
   #	bots/pr/src/test/java/org/openjdk/skara/bots/pr/PullRequestBotFactoryTest.java
 - fix a problem
 - fix problems
 - Merge branch 'master' into SKARA-1852
   
   # Conflicts:
   #	bots/pr/src/main/java/org/openjdk/skara/bots/pr/CheckWorkItem.java
   #	bots/pr/src/main/java/org/openjdk/skara/bots/pr/PullRequestBot.java
   #	bots/pr/src/main/java/org/openjdk/skara/bots/pr/PullRequestBotBuilder.java
   #	bots/pr/src/main/java/org/openjdk/skara/bots/pr/PullRequestBotFactory.java
   #	bots/pr/src/test/java/org/openjdk/skara/bots/pr/CheckTests.java
   #	bots/pr/src/test/java/org/openjdk/skara/bots/pr/PullRequestBotFactoryTest.java
 - Update bots/pr/src/main/java/org/openjdk/skara/bots/pr/CheckWorkItem.java
   
   Co-authored-by: Erik Joelsson <37597443+erikj79 at users.noreply.github.com>
 - fix a problem
 - SKARA-1852

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

Changes: https://git.openjdk.org/skara/pull/1497/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1497&range=02
  Stats: 84 lines in 6 files changed: 80 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/skara/pull/1497.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1497/head:pull/1497

PR: https://git.openjdk.org/skara/pull/1497