Allow for configuring interceptors on generic client (#2697)

## Description
This PR allows users to pass-in interceptors to a generic client.
Client-level configured interceptors are eventually added to
`client_interceptors` and operation-level interceptors to
`operation_interceptors`, both of which are fields in the
`aws-smithy-runtime-api::client::interceptors::Interceptors`. The
relevant code is generated only in the orchestrator mode.

The SDK registers a default set of (client-level & operation-level)
interceptors, and the passed-in interceptors by a user will run _after_
those default interceptors.

## Testing
- Added integration tests `operation_interceptor_test` and
`interceptor_priority` in `sra_test`.

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Co-authored-by: Yuki Saito <awsaito@amazon.com>
Co-authored-by: John DiSanti <jdisanti@amazon.com>