Simplify Jira Connect test setup

What does this MR do and why?

This adds some configs to enables testing the Jira connect app in a development environment. The app usually requires:

• A Jira Cloud instance.
• A GitLab instance available over the internet. For example via Gitpod

With the config changes, it will be possible to install the app via the Jira connect test tool which simulates a Jira environment.

Related issue: #383157 (closed)

Screenshots or screen recordings

How to set up and validate locally

1. Follow the simple setup documentation added with this MR.
2. You should see the GitLab for Jira app start page.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.