Create system note when issue contacts are changed

What does this MR do and why?

Related to #349683 (closed)

When crm contacts are added/removed from issues, system notes are now created.

Screenshots or screen recordings

How to set up and validate locally

0. Enable :customer_relations feature flag for a group via the rails console
1. Visit the group settings page (e.g. http://gdk.test:3000/groups/flightjs/-/edit
2. Expand "Permissions and group features"
3. At the very bottom, select "Enable customer relations"
4. Select "Save changes"
7. Create some contacts (customer relations -> contacts) *if you've recently setup GDK or reseeded your database, there should already be some setup!
8. Add and remove some contacts to/from an issue using the "/add_contacts email@example.org email2@example" and "/remove_contacts email3@example.com email4@example.com" quick actions
9. Wait a few seconds... hopefully the system note will appear

MR acceptance checklist

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