Support single files for attestation

[francislavoie]

Wrapping the $dir condition with is_dir, otherwise it throws a PHP warning if a string that isn't a directory is passed to opendir. Adds an elseif to check if the path is a valid file, if so add it to the files list.

This is the minimal possible changeset for this, I can add tests if needed. I think $attestDir can be renamed to $attestPath to better match what it does, if this is a change you'd be open to merge. Please let me know if I should make those additional changes.

[klali]

LGTM. A test would be nice if you can add.

[francislavoie]

Sorry it took so long, added a test.

It's just the same test as the one right above, except uses the path to the .pem file directly instead of the parent directory. I ensured that the test fails without the change to get_certs.

[klali]

Thanks! merging.