Add easier way to toggle between terraform-ls / terraform-lsp but keeping auto-updating

[paultyng]

While the feature sets are diverge more significantly, it may be useful to let users easily opt between language servers (but retaining installation and auto-updating). This should still default to the terraform-ls option.

[paultyng]

I think we probably need a few UI options and some advanced options for this:

UI Options:

• Language Server: hashicorp/terraform-ls (Default), juliosueiras/terraform-lsp, Manual (set path in advanced), None

Advanced Options

• Path to binary (for Manual only)
• Args (for any ls)

Manual would require you to specify a path for it to work, otherwise would have a warning or error.

For terraform-lsp it should use the GitHub release auto updating functionality if possible.

[paultyng]

We need to make sure for the binary path, we are considering the scoping, it probably needs to just be machine, I have issues with the current scoping when I toggle between Windows/WSL.

[jpogran]

We now include terraform-ls in the extension VSIX, so we do not update terraform-ls out of band.

Scoping of machine related settings has been adjusted in #1164, so that part is taken care of now.

VS Code separates extension settings by leading identifier, so terraform.languageServer.pathTobinary is technically a different extension setting than terraform-ls.rootModules. This is an somewhat unwritten convention that is upheld by every extension in existence. We've standardized all the extension names in #1156, so any language server planning on integrating with this extension should use the terraform.languageServer* settings provided here or request an additional setting added for their extension.

This ticket is complete

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