feat(nimbus): Add cancel emoji if requests get cancelled

[yashikakhurana]

Because

• Users can cancel launch requests and resubmit them. However, we don’t have any indication in Slack messages that a request has already been cancelled, so reviewers aren’t aware of this.

This commit

• Adds the cancel emoji to the requests if the request is already cancelled
• This also fixes to look for the latest request for the emoji to add as we have seen it tried to add emoji to the old requests

Fixes #14840 #14838

using single method now

[jaredlockhart]

Yeah we should have an enum somewhere of all the slack emojis we want to send and use but otherwise very nice good test coverage, very clear 🙏

changes done

[jaredlockhart]

Yeah this reads much better now ty @yashikakhurana 🎉 🎉 🎉 🎉