Allow customizing service name in service options

[sagikazarmark]

This is supported in TypeScript and Python and I've been using that feature to run the same service with different configuration in the same Restate env.

Some use cases:

• "Priority" or dedicated instance based on customer
• S3 object interface talking to different object stores (different endpoints)

Not sure if this is even feasible, haven't checked the code yet. I couldn't find a similar issue, so I thought I'd start a discussion first.

[sagikazarmark]

Gave it a try in #80