Clean up JiraService
What does this MR do?
It implements the steps proposed in https://gitlab.com/gitlab-org/gitlab-ce/issues/24967 that make JiraService code more understandable and aligned with other project services. It also prevents making unnecessary calls to JIRA API by ProjectServiceWorker . Also, https://gitlab.com/gitlab-org/gitlab-ce/issues/24777 will no longer happen after these changes.
Are there points in the code the reviewer needs to double check?
Does this MR meet the acceptance criteria?
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Changelog entry added [ ] Documentation created/updated[ ] API support added- Tests
[ ] Added for this feature/bug-
All builds are passing
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Conform by the merge request performance guides -
Conform by the style guides -
Branch has no merge conflicts with master(if it does - rebase it please) -
Squashed related commits together