feat: file extension tags

[cgetzen]

Description

This introduces the ability to tag torrents based on file extensions with a new configuration option "file_extension" that matches the format of "tracker". For example:

file_extension:
  iso:
    tag: ISO
  rar:
    tag: [RAR, Archived]
  tar.gz|tar.bz2|tar.xz:
    tag: Tar

Fixes: #641

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the docstring for new or existing methods
• I have modified this PR to merge to the develop branch