Draft: Add sidebar to individual Jira Issue show

What does this MR do?

Adds Assignee, Due Date and Reference sections to the Jira Issues sidebar

This is an iteration towards #298724 (closed)

⛳ This feature is behind feature flag jira_issues_show_integration

How to test (optional)

Prerequisites

• A Jira Cloud account (how do I get this?)

In Jira

1. Create a Jira issue

In GitLab

1. Set up Jira integration with GitLab: https://docs.gitlab.com/ee/user/project/integrations/jira.html
2. Navigate to the Jira Issues section of your project: https://docs.gitlab.com/ee/user/project/integrations/jira.html#view-jira-issues
3. Append the issue reference (i.e. AP-1) to the URL, and load the page - this will manually navigate you to the individual Jira page
4. Observe

Notes

TODO

• Assignee
• Due Date
• Labels
• Reference

Assignee minimum data

        {
          username: 'tomquirk',
          id: '12345',
          can_merge: true,
          name: 'Tom Quirk',
          web_url: 'https://gitlab.com/tomquirk',
          avatar_url:
            'https://assets.gitlab-static.net/uploads/-/system/user/avatar/259327/avatar.png?width=23',
        },

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team