CodeLens: Add `jb` support

An operation that has to be done quite often for jsonnet projects is to interact with dependencies. A very common package manager for jsonnet is the [jsonnet bundler](https://github.com/jsonnet-bundler/jsonnet-bundler).

The language server could have CodeLens buttons (a-la-gopls) to check for updates and if there are any, buttons to update dependencies. That would prevent users from having to call `jb` directly

Start by locating the language server's existing CodeLens handling and the integration point for invoking jsonnet-bundler's `jb` commands. Define how dependency checks and updates should appear as CodeLens actions, then verify that users can check for updates and update dependencies without calling `jb` directly.

Written by the indexing model from the issue text.