Improve language server implementation (configuration handling)

[Shikachuu]

To further improve the language server protocol:

• we should use the InitializationOptions to get the configuration from the client side (which should be parsed/validated in this case) and merge it in viper.
• also we need to implement workspace/didChangeConfiguration which is used to update the running configuration in the server (this also should be parsed/validated) and merged with the running viper config.

With this options you would be able to dynamically reconfigure vacuum through the json rpc protocol from the client side.

If this should be a recommended way to configure vacuum is also an acceptable opinion, imho in that case this functionality should expose only a "configuration-file" option, to be able to use different configuration files like when you run vacuum as a cli app.

[daveshanley]

https://github.com/daveshanley/vacuum/blob/main/language-server/config.go

The vacuum configuration file is correctly picked up by the language server now.

Still need to implement the reload handler though.