Use "Linked issues"/"Linked pull requests" for has_issue/has_pr labels

[mkrizek]

Currently we look at cross-referenced events to determine whether we add has_issue/has_pr but we do not know if those pull request references are considered as possible fixes to given issue (and vice versa) or if they just mention the issue/pr.

With the addition of "Linked issues" and "Linked pull requests" features in Github it might be a good time to re-evaluate implementation of how the bot adds has_issue/has_pr labels. Once the information is exposed in Github API we should investigate if we can make the detection better.

ansible/ansible#72377

[mkrizek]

https://docs.github.com/en/graphql/reference/objects#pullrequest now has closingIssuesReferences.