feat: Support arguments to scripts

[lucinvitae]

Adds support to specify arguments for gen-files plugin as per this unmerged PR from last year:

plugins:
  - search
  - gen-files:
      scripts:
        - path: gen_pages.py  # or any other name or path
          args: "--foo bar"  # the full set of arguments

The only additional changes I added were fixes to merge conflicts.