Replaces Octopus.Shellfish with directly using Process

[geofflamrock]

Fixes #282

Part of a series of PRs that are adding support for AOT:

• Convert to System.CommandLine #276
• Use source generator for Json serialization #285
• Update to Spectre.Console.Cli 0.50.0 #280
• Replaces Octopus.Shellfish with directly using Process #284
• Update to Humanizer.Core v3 beta #286
• Enable publishing with Native AOT #287
• Enable trimming during publish #288
• Remove Humanizer #290
• Update readme to reflect new command options #297
• Remove --working-directory alias #298