Add ability to set log-level in consul client

Currently there is no way to update consul client config to set log-level.
Add a new config option log-level with defaults to INFO in charm and use this option to update log-level on consul client configuration

No file or test is named; start at the charm's config declaration and the code that creates or updates the Consul client. Trace how config values reach the client, then verify that the new log-level defaults to INFO and updates the client's setting when configured.

Written by the indexing model from the issue text.