Implemented server keep alive setting and usage in connect

[andsel]

Release notes

Added configuration setting so that the broker can specify a keep alive other then the one selected by clients.

What does this PR do?

Updates the configuration harness to expose a duration setting name server_keep_alive.
Updated the connAck properties creation to include server keep alive if the broker configuration has selected it.
Updates the connect processing to leverage the server keep alive selected keep alive instead of the client one.

Why is it important/What is the impact to the user?

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works
• I have updated the Changelog if it's a feature or a fix that has to be reported

Author's Checklist

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How to test this PR locally

Related issues

• Closes Server can define its own Keep Alive in CONNACK #789

Use cases