Add path based routing support for docker

[maxemontio]

Hi!

I noticed that terraform provider doesn't have the option to enable path based routing, which i would like to have for my repos.
I have already made changes to the provider locally for testing and was able to change the setting:

curl -su admin https://nexus-mirror.xxx/service/rest/v1/repositories/docker/proxy/mirror.gcr.io | jq .docker
Enter host password for user 'admin':
{
  "v1Enabled": false,
  "forceBasicAuth": true,
  "httpPort": null,
  "httpsPort": null,
  "subdomain": null,
  "pathEnabled": true
}

This feature is desired

[anmoel]

please use a pointer if the value can be empty/nil

[maxemontio]

Hi @anmoel!
It would be nice to have you here to check it again