[serve] Move route to deployment options

[edoakes]

Why are these changes needed?

Move the route_prefix option to @serve.deployment so it can be updated independently of the underlying code.

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[zhe-thoughts]

@edoakes Do you mean "router"?

[edoakes]

@zhe-thoughts no, I meant route (it's called http_prefix in this PR because I can't settle on a name for it yet :)). It's just moving the option from the @serve.ingress decorator to the @serve.deployment one so it can be updated, changed, etc.

[edoakes]

@simon-mo thoughts on the naming for this option? Three options I can think of are: route_prefix, http_prefix, and path_prefix. path_prefix seems like it might be a bit confusing to some users (e.g., is it a filepath? is it a path to my model?). http_prefix is ok but kind of redundant and couldn't be used for another transport type in the future (not a hard requirement). I'm leaning towards route_prefix because it's most similar to the existing API.

[simon-mo]

How about just prefix?

[simon-mo]

LGTM