Create dedicated Cause for MCP

[batmat]

This is useful for the end user to understand that the call was trigger through this plugin's code and not some manual user intervention. And among others, it allows plugins like buildtriggerbadge to offer custom badges.

Testing done

Before this change, if you trigger the build through the MCP Server, this would show this (because the code was using "UserIdCause")

With this change

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch! (opened from my own fork and dedicated branch)
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira (didn't create one, as this sounded like a very small change, but happy to create one if needed)
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed (manually tested, but I can write an automated test if desired)

[batmat]

🤔 Now I realize that keeping also the username who is using the MCP server would be important. I'll modify the PR.

[olamy]

🤔 Now I realize that keeping also the username who is using the MCP server would be important. I'll modify the PR.

moved it to draft for now