Consider give `RequestContext.addRequestCallback` a better name

The API name `addRequestCallback()` in `RequestContext` is a bit confusing, the name to me is that the callback will be executed after the request being sent, because usually a callback is executed when something complete. But in fact, this callback will be executed before the request being sent.

code here: https://github.com/Azure/azure-sdk-for-java/blob/main/sdk/clientcore/core/src/main/java/io/clientcore/core/http/models/RequestContext.java#L249

Potential name: `addBeforeRequestHook()`