Show PR experiment info in Cloud Build Page.

Currently, we have to write down the [experiment report and data info](https://github.com/google/fuzzbench/pull/1984#issuecomment-2123668690) manually. This is annoying because the experiment trigger always parses the last comment, so we must wait until the experiment has launched before pasting the links.

This [PoC](https://github.com/google/fuzzbench/pull/2007) shows a way to automate this, which [prints the PR ID](https://github.com/google/fuzzbench/pull/2007/checks?check_run_id=28085580685#:~:text=Step%20%230%3A%20PR%3A%20%25s%202007) as an example. We can extend the code to show the experiment report and data.