(client) Create a client for a runtime service fails for missing env

[leorossi]

We are aware that a Platformatic runtime has a single .env file at the root of the projects.

All services env variable are prefixed with PLT_SERVICE_NAME_... in that file.

Having a service called foobar having some env variables in its platformatic.json file, the command platformatic client --runtime foobar because it doesn't load the .env from the root directory apparently and complains about missing env variable