Add in a section about sbt BSP server and differentiate it from current server page.

[ckipp01]

Something I've seen a few Metals users stumble on (and I've done it myself before), is to assume that the sbt-server page is where they should look for information about the sbt BSP server. Even though I know this page is about the LSP server, I've even accidentally linked this before when quickly searching the sbt sidebar and I see server and I assume this is what I want.

I'm not sure what the status of the sbt server is, but it would be great to have a specific page about the sbt BSP server and make it very clearly differentiated by the current sbt-server page.

[eed3si9n]

I think we should keep using sbt server page, but put relevant information about BSP.

[eed3si9n]

I've added Metals instruction on the same page - #980