Allow group operation on fine-grain loggers from adminz

Envoy has 2 logging management systems, the traditional one and the fine-grain file-based one.

https://www.envoyproxy.io/docs/envoy/latest/operations/admin#post--logging

The fine-grain logger provides the powerful file based logging management, but when we want to change the logging level, it is not user friendly like the traditional sub-system. One idea to improve it is to have a predefined map to achieve:

/logging?group=htttp:trace

so the group http will apply some log level setting to all the core http files in the predefined map to simplify the usage.