Support separate configs per character

[kalilistic]

Add an option to enable separate plugin settings per character.

Some ideas / considerations from discussion in discord:

• Make this all or nothing to keep things simple
• Make the change early to avoid downstream impacts (i.e. xivlauncher / player config directory / chr_abc123 / normal files)
• On enabling this feature, prompt to copy files from regular config directory
• Need to decide what to use for the character directory (chr_abc123) - name/world, cid, something else?

https://discord.com/channels/581875019861328007/860813266468732938/879071152662806578