Warn users if no lockfile is detected on the configured workspace

[vinistock]

Motivation

Closes Shopify/ruby-lsp#1691, closes Shopify/ruby-lsp#1693

The change to support multi-root workspaces is causing some confusion for users. Previously, because we always activated the LSP on the first workspace folder entry, the LSP would "work" even in a monorepo without proper multi-root configuration. It would not find the bundle and then just start as if you had none.

Now, with adequate multi-root support, we don't activate if the workspace doesn't include a bundle. We can do better to direct users into applying the proper configurations.

Implementation

My proposed solution is to show a warning when we try to activate the LSP in a workspace that doesn't contain a bundle, allowing the user to take 3 actions:

• Launch the LSP anyway. This will simply ignore the fact that we didn't find a bundle and the LSP will be launched on its own. This is still useful for scripts
• See the documentation for multi-root workspaces and monorepos, so that they can configure VS Code to identify each directory as a workspace
• Permanently ignore this warning and always launch the LSP