Allow log level to be set and filtering logs accordingly

[obourdon]

Checklist

• [x] make test-all (UNIX) passes. CI will also test this
• [ ] unit and/or integration tests are included (if applicable)
• [x] documentation is changed or added (if applicable)

Description of change

Some of the goss default logging messages might be seen as not very useful. This fix allow easy log level customisation and filtering

Reopen of PR https://github.com/goss-org/goss/pull/641

[obourdon]

Only real comment is if we can expose these new config items in the embedded scenarios

not sure I fully understand what you meant here or may be this is related to what you wrote later concerning programmatic reconfiguration

[aelsabbahy]

I am ok with merging as is. I am the main user of the embedded behaviours (that this enables) so can also propose a follow up PR for that

Thank you for the review.

@obourdon thank you for taking the time to submit this PR.. twice (apologies for that)