Resolve "Add colors for user tokens in escalation policy modal and view"

What does this MR do and why?

Describe in detail what your merge request does and why.

• uses util function from ee/oncall_schedules to assign the same colour palette to escalation rules participants
• maps all selected users and sets styles to their tokens based on the order of appearance on the escalation policies view / modal

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

before	after

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Prerequisite:

You must have at least the Maintainer role. You must have an on-call schedule. To create an escalation policy:

1. On the top bar, select Main menu > Projects and find your project.
2. On the left sidebar, select Monitor > Escalation Policies.
3. Select Add an escalation policy.
4. Enter the policy’s name and description, and escalation rules to follow when a primary responder misses an alert. Choose a specific user to be notified.
5. Select Add escalation policy.
6. Select Edit escalation policy.
7. Add additional user to be notified.

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 #335680 (closed)