`EE_PROXY_TYPE` to be replaced by a utiliy function

Currently, EE_PROXY_TYPE is a constant, which is the container id of the global nginx-proxy container. It is computed every time during the initialization of an command as it is present in the runner.

The command executed for it is time consuming and also required by only a handful of commands, hence it should not be in the runner. Instead it can be replaced by a utility function which computes it's value only when required.

Once the value is found for the first time, it can be stored in a constant, and on next call is_defined function can be used in the function to check if the value is already there, to skip the time consuming computation for the second time.