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 ⚠️
source/client.c	0.00%	3 Missing ⚠️
source/v5/mqtt5_to_mqtt3_adapter.c	0.00%	3 Missing ⚠️
source/client_impl_shared.c	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            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.