Add Code Coverage tracking using SonarCloud

[Ndiritu]

microsoftgraph/msgraph-sdk-php-core#5 add code coverage tracking to the Core library.

This can be improved by making Code Coverage analysis a stand-alone PR validation step. This would need consideration of existing 3rd party open source & proprietary tools vs custom scripting to do this

Would also be a bonus to add a coverage badge to our README
AB#10694

[Ndiritu]

SonarCloud was recommended during Michael's compliance work.

[SilasKenneth]

Yes, I have added a coverage badge to other repositories. I'll be adding it to core once the repo is added to SonarCloud.