Allow for specifying extra class paths to embedded server.

[supernomad]

This wires in the extra_classpath argument from start_jvm to the constructor for the Server instance. This will allow for users to easily write python unit tests that can interact with custom Java implementations as well.

[devinrsmith]

LGTM. I don't see this conflicting with #5275, or future ambitions of sourcing defaults from environment variables. Tagging @niloc132 for review.

[mofojed]

Looks good to me... any reason we should accept any of the other parameters?

        jvm_properties = None,
        java_home = None,
        extra_classpath = [],
        propfile: str = None,
        config = None

[supernomad]

Looks good to me... any reason we should accept any of the other parameters?

        jvm_properties = None,
        java_home = None,
        extra_classpath = [],
        propfile: str = None,
        config = None

I am more than happy to add wiring for all of these if we want, won't take me long so let me know!

[devinrsmith]

Looks good to me... any reason we should accept any of the other parameters?

        jvm_properties = None,
        java_home = None,
        extra_classpath = [],
        propfile: str = None,
        config = None

I might prefer to expose less for now to give ourselves the flexibility to change in the future if we need to. For example, I think setting an explicit propfile is bad practice, and we should prefer to inherit it based on the configuration dir.

[niloc132]

LGTM

[chipkent]

LGTM