Use enum instead of boolean for eagerlyReadResponse

[kasobol-msft]

Today, RestProxy takes care of disposing response if there's no need to process body, i.e. there's Response<Foo, Void>.

Related code:

azure-sdk-for-java/sdk/core/azure-core/src/main/java/com/azure/core/http/rest/RestProxy.java

Line 475 in 627f107

return response.getSourceResponse().getBody().ignoreElements()

and

azure-sdk-for-java/sdk/core/azure-core/src/main/java/com/azure/core/implementation/serializer/HttpResponseBodyDecoder.java

Line 393 in 627f107

public static boolean shouldEagerlyReadResponse(Type returnType) {

We can (probably) simplify this logic a bit by introducing enum to cover the requested response type and also release a connection a little bit faster.
We can consider an enum ResponseBodyReadStrategy { EAGER, STREAMED, NO_RESPONSE_BODY } and take care of that handling at http client layer instead in rest proxy.
Something like:

[alzimmermsft]

This is a more in-depth handling of the current design which is .ignoreElements() to get doFinally() to trigger and close the connection. It also triggers eagerly, so we free the resources sooner.

[alzimmermsft]

If this goes well in sync stack, or is determined to be a larger issue rather than resolving an edge case and making this more eager, this will be propagated from the sync stack feature branch sooner than when sync stack will land.

Note, this isn't blocked by sync stack, nor needs to be done as part of it.