chore: promote guidobrei to java approver

[toddbaert]

@guidobrei has consistently attending meetings, offered contributions to the Java SDK and java-contrib, and has been a consistent, high quality reviewer.

This PR promotes him to Java approver.

Thanks so much for all your energy and efforts!

@guidobrei please :+1: or approve this PR to signal your interest in this role.

Note that @guidobrei is from my company, Dynatrace, so we will require an approval from a non-Dynatracer as well.