Jira Issue detail serializer and entity

What does this MR do?

At the moment, we can see the "Jira Issue List" (see Jira issues within GitLab), here we are referring to view one of the individual items. This adds the "Jira Issue Detail" serializer and entity to support the frontend work from !52446 (merged), !52792 (merged), !53044 (closed), etc.

This retrieves a Jira issue using the Jira API V2 and returns the JSON to be consumed by the frontend.

The "Jira Issue Detail" page is under a feature flag jira_issues_show_integration but this is how looks at the moment from this branch but we expect to iterate over this in future merge requests.

Jira	GitLab

Related to #294155 (closed)