Documentation: update Komga widget instructions with api key instructions

[ameerabdallah]

Proposed change

Update komga docs with api key generation instructions

Closes #4126

• New service widget
• Bug fix (non-breaking change which fixes an issue)
• New feature or enhancement (non-breaking change which adds functionality)
• Documentation only
• Other (please explain)

Checklist:

• If applicable, I have added corresponding documentation changes.
• If applicable, I have reviewed the feature / enhancement and / or service widget guidelines.
• I have checked that all code style checks pass using pre-commit hooks and linting checks.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.

[ameerabdallah]

noticing some funny business with api tokens and komga. closing until I can figure out what is causing it

[ameerabdallah]

looked into it and it looks like it actually needs a Bearer auth to use the api key. not sure why it worked when I was testing it at first though, config must have been saving the wrong file or something.

Would require changes to the widget itself to get #4126 closed.