Pls adopt the extensionKind format

[egamma]

As of VS Code 1.40 the extensionKind attribute in the package.json of the extension can be an array, pls see the documentation.

We will be deprecating the string type for extensionKind property in favour of string array type.

The extensionKind attribute for the settings sync extension should be set to ["ui"]. Indicating that the extension must run locally as a UI extension.