feat: added configuration options via Environment

[Nold360]

Here are more additions for containers (mostly):

This change adds 3 Environment Variables:

ENV MT_CONFIG_PATH "/bin/mapserver.json"
ENV MT_LOGLEVEL "INFO"
ENV MT_READONLY "false"

MT_CONFIG_PATH allows to specify the exact location for the config.
MT_READONLY has been introduced because i used a k8s configmap for my configuration. Making it Read-Only.

[BuckarooBanzay]

out of curiosity: how do you deploy the mapserver to k8s, do you use tags/releases or are you using the latest tag?

[BuckarooBanzay]

fyi: had to adjust the default mapserver.json location to the current dir: 073647a (without /bin prefix)