CONNACK set shared subscription available property to true

Release notes

Updates the CONNACK message's property shared subscription available to return reflect the availability of the functionality

[x] 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~~
[x] I have updated the Changelog if it's a feature or a fix that has to be reported