Allow passing different arguments to different postprocessors

* Also deprecated --sponskrub-args

Closes: https://github.com/ytdl-org/youtube-dl/issues/27593
Eg: `--postprocessor-args "VideoConvertor:-c:v h264_nvenc -preset slow"`
Eg: `--postprocessor-args "SponsKrub:-include-selfpromo"`

For backward compatibility, `--postprocessor-args args` is equivalent to:
`--post-processor-args "sponskrub:" --post-processor-args "default:args"`

youtube_dlc/postprocessor/execafterdownload.py

@@ -11,6 +11,8 @@ from ..utils import (
 
 
 class ExecAfterDownloadPP(PostProcessor):
+    PP_NAME = 'Exec'
+
     def __init__(self, downloader, exec_cmd):
         super(ExecAfterDownloadPP, self).__init__(downloader)
         self.exec_cmd = exec_cmd
@@ -22,7 +24,7 @@ class ExecAfterDownloadPP(PostProcessor):
 
         cmd = cmd.replace('{}', compat_shlex_quote(information['filepath']))
 
-        self._downloader.to_screen('[exec] Executing command: %s' % cmd)
+        self.to_screen('Executing command: %s' % cmd)
         retCode = subprocess.call(encodeArgument(cmd), shell=True)
         if retCode != 0:
             raise PostProcessingError(