Remove usage info from log output

[bjee19]

Remove usage info from log output.

Problem: When a critical error occurs at startup, usage information for the binary is dumped into the log output.

Solution: Set SilenceUsage and SilenceErrors to true in the root cobra.Command. This problem was discussed here in an older discussion on cobra's github page.

Testing: Manually tested these cases (usage is there before the change and is no longer there after the change):

• Running docker restart kind-control-plane which displayed the error recorded in a non-functional test here.
• Not creating the NginxGateway CRD on startup.

Please focus on (optional): Should I set SilenceUsage in createProvisionerModeCommand? Currently its just in the StaticModeCommand. Also, as described in the discussion linked above, it mentions possibly setting SilenceUsage in the root command, should I instead put that in createRootCommand?

Closes #1105

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[kate-osborn]

I think we should also set SilenceError to true so we don't print the error message twice:

without SilenceError:

{"level":"info","ts":"2023-11-10T14:24:48-06:00","msg":"Starting NGINX Gateway Fabric in static mode","version":"edge","commit":"fbc33116eba7fc8e52c55dedb073d97bf8d00995","date":"2023-11-10T20:19:02Z"}
Error: error validating POD_IP environment variable: IP address must be set
error validating POD_IP environment variable: IP address must be set

with SilenceError:

{"level":"info","ts":"2023-11-10T14:31:26-06:00","msg":"Starting NGINX Gateway Fabric in static mode","version":"edge","commit":"fbc33116eba7fc8e52c55dedb073d97bf8d00995","date":"2023-11-10T20:30:42Z"}
error validating POD_IP environment variable: IP address must be set

Should I set SilenceUsage in createProvisionerModeCommand? Currently its just in the StaticModeCommand. Also, as described in the discussion linked above, it mentions possibly setting SilenceUsage in the root command, should I instead put that in createRootCommand?

I think it makes sense in the root command so that every subcommand inherits those values.