Add prefix to pipeline trigger tokens to make them easier to scan for an detect leaks

Proposal

Like many of our peers in the industry we've been adding prefixes to some of our tokens (personal/project/group access tokens, runner registration tokens). Next in line for this effort would be the pipeline trigger tokens. We've had issues in the past where such tokens were leaked and adding a prefix would help our detection mechanisms and help our security teams detect and prevent leaks more effectively.

I suggest a glptt- (ptt for pipeline trigger token) prefix but it can be anything as long as it's easy to search for!