Protocol adapter skeleton

[bretambrose]

• Request-response protocol adapter interface
• MQTT5 specific implementation of the request-response protocol adapter interface

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: 33 lines in your changes are missing coverage. Please review.

Comparison is base (171840f) 82.54% compared to head (38532f0) 82.55%.

Files	Patch %	Lines
source/request-response/protocol_adapter.c	84.07%	25 Missing :warning:
source/client.c	0.00%	3 Missing :warning:
source/v5/mqtt5_to_mqtt3_adapter.c	0.00%	3 Missing :warning:
source/client_impl_shared.c	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #342 +/- ## ========================================== + Coverage 82.54% 82.55% +0.01% ========================================== Files 20 22 +2 Lines 8763 8949 +186 ========================================== + Hits 7233 7388 +155 - Misses 1530 1561 +31 ```

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[sbSteveK]

We might want to update mqtt5_client.h "@param completion_options" to include a short description of the recently added ack_timeout_seconds_override members since the options aren't really addressed anywhere else. We could also include somewhere in the code comments or some documentation around the request-response various option structs what's up with the ack_timeout_seconds each has and what its default value does. Mostly for ourselves in case we're looking.