QOL: Add support for cli argument --custom-nodes-directory

[Sasbom]

Retry of #10647 .

Closes #10646

Implementation of changes proposed in linked issue.

• Read --custom-nodes-directory in comfy.cli_args
• Support multiple folder entries by including a platform correct ';' / ':' delimiter, e.g.
  --custom-nodes-directory "/path/to/folder1;/path/to/folder2" on windows.

Fixes import reorder / unnessecary documentation.

Thanks for your consideration,

Sas