Consider moving SignalR maven repo signing into signtool or a specialized VMR build.

[mmitche]

SignalR signing is done in two stages today: Normal ESRP signing in signtool, then a specialized GPG sign step required to push to the maven repo. The latter lives in the staging pipeline. Consider supporting this in signtool, or alternatively, just running this in the VMR build pipeline when building release/*.

[mmitche]

SignalR signing possibly could be done in signtool, but I think we should keep this in the staging piepline for P4. The jar file signing is working, but there is an additional step where we take aspnetcore's maven gpg private key and sign the packages. This is not an ESRP step. We could move it into the VMR, either in signtool as a special kind of signing, or in some post-build step. I favor the former? Maybe. Either way, I am considering this not critical for p4.