Add support for specifying a command in browser configurations

[Overbryd]

• Introduce a new command option in BrowserOpts to allow specifying a custom command to open URLs.
• Update AppDescriptor and relevant methods to handle the new command type.
• Modify the getBrowserCommand function to prioritize command over app paths and bundle IDs.
• Update configuration schema validations to include the new command attribute.
• Add logging for URLs, bundle IDs, and app paths for better debugging.
• Bump CFBundleVersion from 319 to 336 in Info.plist.

[johnste]

This looks interesting! I'm about half way through a rewrite of Finicky, and I'll have a closer look at this in a bit.