add missing `--help` cmd option

[sebastianwebber]

Is your feature request related to a problem? Please describe.
pgcat cmd misses the --help option. by default, no log message is displayed, and for non-rust programmers, there is no way to know what is going on except by changing the RUST_LOGenv var. This issue aims to fix this problem.

Describe the solution you'd like
Already added a PR to add command line options for the config file and the log level.
#512

[sebastianwebber]

since the PR was merged i'm closing this issue.