Add strip markup to incident title

What does this MR do and why?

Fixes the suggestion mentioned in !105760 (comment 1259074069)

Screenshots or screen recordings

NA

How to set up and validate locally

1. Follow the steps mentioned in https://gitlab.com/gitlab-org/manage/integrations/team/-/blob/main/integrations/slack.md to setup slack dev env.
2. Open the incident modal using /dev-gitlab incident declare
3. Use a link in the title input
4. Check the created incident response in slack does not contain the link tags.

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.