chore(contributions): respect vscode standards

[innocenzi]

This PR slightly updates package.json's contributions section to better align the the standards described in the Code documentation.

Specifically:

• In commands, use category instead of manually prefixing Phpactor:
• In configuration, use a title corresponding to the project name
• In configuration, fix the schema types
• In commands and configuration, update the descriptions

Hope I'm not overstepping here

[dantleech]

thanks!