Provide configuration page

[yaohaizh]

GITLENS provides its extension own setting page:

https://github.com/eamodio/vscode-gitlens#configuration

Java extension has the similar requirement for the settings page to provide a user friendly UI and advanced features besides VSCode default setting editor:

1. Code templates
2. Formatting
3. Settings from language server
4. Tweak for performance
5. Other customizable behavior.

[ayushbhatt2000]

Hi! I wanted to contribute to this issue, can you tell me how to do so?