Support ClickUp as an issue tracker

What does this MR do and why?

Support ClickUp as an issue tracker

Add a new integration for ClickUp project management as a new external issue tracker.

Supported formats for issues:

• #abcd1234
• CU-abcd1234
• PRJ-1234

Changelog: added

Screenshots or screen recordings

Integration configuration:

Linked issues in commit message:

Linked issues in an internal GitLab issue:

How to set up and validate locally

1. Enable the ClickUp integration in Project > Settings > Integrations > ClickUp
2. Set the project URL (e.g. https://app.clickup.com/1234567) and a the issue URL (e.g. https://app.clickup.com/t/:id)
3. Create a commit/issue/wiki etc where external issue IDs can be used. Use either the format #abcd1234 (a # followed by a lowercase alphanumerical ID; OR use the global prefix by substituting # for CU-; OR use the custom prefix format PRJ-1234. The prefix must be 2-10 characters, and consist of capitals, numbers, or underscores. The ID must be numerical.

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 #411254 (closed)