add execution_method in *_sources.json and forge_register -executionMethod

[godfuzz3r]

now it's possible to select default execution method for assemblies in _sources.json (execute_assembly or inline_assembly):

[
  {
    "name": "ADCSPwn",
    "execution_method": "inline_assembly",
    "command_name": "ADCSPwn",
    "repo_url": "https://github.com/Flangvik/SharpCollection",
    "description": "C# tool to escalate privileges in an active directory network by coercing authenticate from machine accounts and relaying to the certificate service. @bats3c"
  },
  ...

if execution_method not selected - execute_assembly used

Also it's possible to set execution-method with forge_register via forge_register -executionMethod <execute_assembly|inline_assembly>