Improve heartbeat to get better runtimeFramework info.

[cijothomas]

HeartBeat currently uses the following code to get FrameworkVersion, which is not giving any useful information.

#elif NETSTANDARD1_3 || NETSTANDARD2_0
            return System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription;
#else

With the new change in .net core itself, we'll see better information starting 3.0.
dotnet/corefx#35516

We need to do something more useful for non 3.0 customers. Goal is to return something like '.net core2.1' or 'netfw4.7' m for heartbeat field "runtimeFramework".

[github-actions]

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