Improve and fix Sonarr general settings configuration updates

[Callum027]

This fixes the remaining issues for pushing configuration updates for Sonarr general settings.

• Fix updates for sonarr.settings.general.proxy.password.
• Improve Sonarr instance authentication username and password handling so that it more closely matches the Sonarr instance state:
  • Sonarr does not set the username and password back to blank values once set to a non-zero value, even when authentication is also disabled.
  • To handle this, implement a validator that enforces the following conditions:
    • When authentication is explicitly disabled in either Buildarr or the remote Sonarr instance, set the username and password to None. This prevents meaningless configuration updates from Buildarr from occurring.
    • Require the username and password to be set to a non-empty value if authentication is enabled in Buildarr.
• Fix a definition of sonarr.settings.general.security.authentication mistakenly set as authentication_method in the documentation.