Add link slash command

What does this MR do and why?

Relates to #374964 (closed)

Adds a /link quick action command that adds any type of resource link to the Linked resources section.

Screenshots or screen recordings

Screen_Recording_2022-10-04_at_1.14.54_PM

How to set up and validate locally

1. Enable the feature flag incident_resource_links_widget using Feature.enable(:incident_resource_links_widget)
2. Make sure you have the premium+ license installed.
3. Make sure you have at least reporter permissions.
4. Create an incident manually by navigating to Monitor > Incidents from the left sidebar menu of your GitLab project.
5. Use the quick action command as shown in the video.

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.

Related to #374964 (closed)