feat: add inlay hints setting

[gAbelli]

Add support for inlay hints settings introduced in Metals v1.3.0.

Reference:

• https://scalameta.org/metals/blog/2024/04/15/thalium#inlay-hints-support
• https://scalameta.org/metals/docs/editors/user-configuration

[ckipp01]

Thanks for adding this @gAbelli! Since we're moving this into inlayHints like they're supposed to be we can also remove the following:

    showImplicitArguments = true,
    showImplicitConversionsAndClasses = true,
    showInferredType = true,

They no longer need to be their own valid keys. While from the looks of it in Metals they are still supported lets only advertise a single (new) way of doing this.

[gAbelli]

I agree, I dropped them from the documentation but I kept them among the valid settings for backwards compatibility

[ckipp01]

Looks good, thanks!