Add doxygen github action to generate doc and doc coverage.

[shamitha-shashidhara]

Generated comprehensive documentation using Doxygen comments. Generated documentation coverage numbers using Covrxygen. Generating DoxygenWarningLog.txt, which includes warnings about undocumented elements.

Files Added
doxygen-build.yml: Workflow file to build the Doxygen documentation.
doxygen-publish.yml: Workflow file to publish the Doxygen documentation.
Doxyfile: Configuration file for Doxygen.
DoxygenMainPage.md: Main entry page for Doxygen documentation.
README.md: Updated to include instructions on how to generate and view the Doxygen documentation.

[frankdarcyacn]

We need to be careful that Doxyfile in this PR does not conflict with the one currently in gerrit's referenceApp workspace main branch - that version has GENERATE_XML=NO whereas in this PR GENERATE_XML=YES (as needed to generate coverage).
Maybe its easiest to set GENERATE_XML=YES in gerrit first, but that would mean that XML is always generated, even when we just want HTML, and it would take twice as long (roughly).
@marcmo - do we know when gerrit will next be synced to github?
Alternatively, perhaps we could leave is at GENERATE_XML=NO and if we want to generate XML for coverage then change it on the command line like this...

sed -i '/GENERATE_XML.*=.*NO/c\GENERATE_XML = YES' ./Doxyfile
doxygen Doxyfile

Just a thought.