Moving to Central package management and enabling NuGet auditing

[joperezr]

• Enabling NuGet auditing to get build errors when one of the packages we depend on is marked as vulnerable.
• Enable Central package management on our src and test directories (not samples). This will allow us to manage package versions centrally and ensure that all projects use the same version of a package, as well as be able to transitive pin when required due to transitive dependencies marked as vulnerable.
• Bump the SDK we use to build to the now released 9.0.100

cc: @twsouthwick