Suggest available Jira issues when editing a Merge Request title or description
## Problem to solve
Having the ability to quickly select from a list of Jira issues when editing a MR title or description would be a nice QOL improvement.
## Related issues
This issue is part of epic to improve the Jira <> Merge Request experience &4637.
Related issues and suggested order of implementation:
1. Add a project-level toggle to require Jira association in Merge Requests gitlab#268294
1. Add Jira ticket association requirement to Merge Requests gitlab#268292
1. Add a project-level toggle to require Jira association in Merge Requests gitlab#268294
1. This issue
## Proposal
1. When the feature flag is enabled.
1. And the project has Jira integration.
1. When a user types in text that matches the an integrated Jira project's code, for example `JRE`.
1. Then show an autocomplete dropdown with the Jira ticket numbers and titles.
1. When a user types in text that matches the start of a Jira ticket, for example `JRE-11`.
1. Then show an autocomplete dropdown with the Jira tickets that match the entered text, for example `JRE-110, JRE-111`.
1. When a user clicks on a suggestion, insert the Jira ticket reference into the textfield.
A note on Jira ticket formatting. The ticket reference is always in all caps, contains a dash and ends in a number.

## Implementation issues
1. ~backend https://gitlab.com/gitlab-org/gitlab/-/issues/352498
2. ~frontend https://gitlab.com/gitlab-org/gitlab/-/issues/352497
epic