Add support for continuation tokens about azure-devops-rust-api

[johnbatty]

Worth noting that the Azure SDK has done some work in this area, notably:

• azure_core::Pageable
• azure_core::Continuable
• initial work to support x-ms-pageable for generated specs
• Sketch for returning headers with responses

Need to decide whether we leverage this or just implement something similar to the Azure DevOps Python package.

[johnbatty]

A recent enhancement to the autorust enables access to headers on responses by using send() on requests rather than into_future(). This allows continuation tokens to be obtained by apps.

I'll update the docs and add an example to show how to do this.

[johnbatty]

Added an example that demonstrates how to do large queries with continuation tokens by using the new send() and raw_response() functions: build_list_continuation_token

[kyle-rader-msft]

@johnbatty I'm curious on your thoughts about also handling pagination for APIs that don't use continuation tokens like the Git Commit Get Changes API, which only uses top and skip params, but doesn't have any indication if there are more results to fetch. You have to just attempt to fetch them yourself.