Make long-running operations consistently return Wait[T]

[nfx]

No description provided.

[pietern]

@nfx I think this should stick to the same rules as applied for the Go SDK, where the basic functions (e.g. create) immediately return the create response, and only the _and_wait functions also do the waiting.

That way all functions that map to our APIs 1:1 return a response and not a custom return type. By having some of those functions return a response and others a waiter can be confusing. By having only _and_wait functions return one of these Wait instances (or directly call result) it's immediately clear if it maps to an API call or if it does additional polling and might block for a while.

[nfx]

@pietern this is a compatibility layer with other clouds SDK and AIP-151 https://google.aip.dev/151, where long-running operations do return a Future/Promise by default.

it’s one of the topics for discussion tomorrow. Also we should send out a customer survey in a month or so, just to gauge community’s preference.