Add new push rules to prevent pushing secrets

Context

We have a super cool push rule to help prevent users from pushing secrets to repositories.

Proposal

We expand the default files_denylist.yml file to include more types of files that really shouldn't be pushed to repositories, according to security best practices.

What to add??

💡 We can review open source projects designed to search public repositories for secrets and see what they are looking for and use this to improve our push rule to provide even more value. (example)

Thx to @WarheadsSE for prompting this