Reduce verbosity option in policy-tester

[brajbou]

Currently, when running policy-tester, the logging is very verbose and hard to read. It would be great to have an option to reduce logging to just a pass/fail output or not report the blob of an attestation (which is super long).

The reason for the this ask is we would like to use the policy-tester in a cronjob and/or gitlab pipeline to report policy failures and currently the job log is so long it can only be opened in "raw mode".

Example:
./policy-tester --quiet or -q

An example output:

• remove DEBUG blah from each line
• remove image name in the validated signature output
• remove Converted signature blob completely

2024-01-26T08:50:25.105-0500 Checking Authority: aws-key
2024-01-26T08:50:27.009-0500 validated signature for authority aws-key got 1 signatures

[hectorj2f]

@brajbou You can configure the verbosity level now: #1414