Server manager should look for remote-cartesi-machine in PATH

[edubart]

Context

Currently the server manager assumes /usr/bin/remote-cartesi-machine is available, but the cartesi machine could have been installed somewhere else, like /usr/local.

Possible solutions

The server manager should not make hard-coded assumptions where the cartesi machine is installed, it should detect this by using environment variables such as PATH , CARTESI_IMAGES_PATH, or even some new environment variable like CARTESI_SDK_PATH in case necessary.