Code signing should not use third party dependencies

**Is your feature request related to a problem? Please describe.**

If we want to take security serious (and thus doing code signing), it should not depend upon third party dependencies.

**Describe the solution you'd like**

I would like these dependencies to be integrated into this project or removed.

**Describe alternatives you've considered**

Not doing code signing

**Additional context**

My [pr](https://github.com/novotnyllc/NuGetKeyVaultSignTool/pull/142) for the NuGetKeyVaultSignTool, is open for 2 years. Because this part of the code uses a preview version of `dotnet 6.0` and I was no longer accepting that.

If these third party dependencies are not vetted and managed the same way as `dotnet sign` the entire command should be treated as **untrusted** in my honest opinion.