Add `-sign` action to build script

[ellahathaway]

As commented in dotnet/sdk#44855 (comment), fsharp's build script does not support the -sign action.

fsharp/eng/build.sh

Lines 8 to 42 in 3dff60a

	usage()
	{
	echo "Common settings:"
	echo " --configuration <value> Build configuration: 'Debug' or 'Release' (short: -c)"
	echo " --verbosity <value> Msbuild verbosity: q[uiet], m[inimal], n[ormal], d[etailed], and diag[nostic] (short: -v)"
	echo " --binaryLog Create MSBuild binary log (short: -bl)"
	echo ""
	echo "Actions:"
	echo " --bootstrap Force the build of the bootstrap compiler"
	echo " --restore Restore projects required to build (short: -r)"
	echo " --norestore Don't restore projects required to build"
	echo " --build Build all projects (short: -b)"
	echo " --rebuild Rebuild all projects"
	echo " --pack Build nuget packages"
	echo " --publish Publish build artifacts"
	echo " --help Print help and exit"
	echo ""
	echo "Test actions:"
	echo " --testcoreclr Run unit tests on .NET Core (short: --test, -t)"
	echo " --testCompilerComponentTests Run FSharp.Compiler.ComponentTests on .NET Core"
	echo " --testBenchmarks Build and Run Benchmark suite"
	echo " --testScripting Run FSharp.Private.ScriptingTests on .NET Core"
	echo ""
	echo "Advanced settings:"
	echo " --ci Building in CI"
	echo " --docker Run in a docker container if applicable"
	echo " --skipAnalyzers Do not run analyzers during build operations"
	echo " --skipBuild Do not run the build"
	echo " --prepareMachine Prepare machine for CI run, clean up processes after build"
	echo " --sourceBuild Simulate building for source-build"
	echo " --buildnorealsig Build product with realsig- (default use realsig+ where necessary)"
	echo " --tfm Override the default target framework"
	echo ""
	echo "Command line arguments starting with '/p:' are passed through to MSBuild."
	}

This action should be added to the script and should invoke arcade's signing infrastructure when uses.