Move the .txt settings to .json

[Plenyx]

As a developer, I want to store data as a JSON file, instead of txt.

This change would be future-proof and easier to maintain than settings in txt files. The settings in txt files include:

• [x] boss_data.txt
• • [x] Save and load from JSON
• • [x] Migrate existing entries to new file
• • [x] Move default values to Resource File
• [x] discord_webhooks.txt
• • [x] Save and load from JSON
• • [x] Migrate existing entries to new file
• [x] remote_pings.txt
• • [x] Save and load from JSON
• • [x] Migrate existing entries to new file
• [x] webhook_teams.txt
• • [x] Save and load from JSON
• • [x] Migrate existing entries to new file
• [x] Cleanup
• [x] Regression testing