Consolidate log level settings to a single CLI option

[achamayou]

We currently have two separate log level settings, which remain from the SGX days:

1. Host log level, set in configuration (logging.host_level): https://microsoft.github.io/CCF/main/operations/generated_config.html#logging
2. Enclave log level, set via CLI flag (--enclave-log-level)

The host/enclave distinction no longer applies, but the reasons for the second option to be in CLI (clear inclusion in the container security policy) remain. So I propose that we move to a single CLI option: --log-level.

This is a user-facing change, and so it must wait for after 6.0 final, since we are now cutting 6.0 release candidates.