Improve UX/docs for updating ruby-lsp when using alongside third-party addons

[andyw8]

Reported via the DX Slack:

"Update language server gem" action doesn't persist if you have ruby-lsp-rspec installed We kept running into "Error while indexing: undefined method `required_positionals'" errors, which was addressed in this issue. It was suggested in the issue to run the Ruby LSP: update language server gem command in VSCode, but this only updated it temporarily. On the next IDE restart, it went back to that error. (The command just appears to do gem install lsp, source.) Looking into the .ruby-lsp/Gemfile.lock, we saw that the versions in the Gemfile.lock were not updated. >Running bundle update ruby-lsp didn't do anything; the gem version stayed the same, because ruby-lsp-rspec was blocking higher versions. Only running bundle update ruby-lsp ruby-lsp-rails ruby-lsp-rspec actually solved the issue. Not sure if that means the command should use bundle instead, or if the ruby-lsp-rspec gem needs to have different semver constraints. Hope this helps and thank you for fixing the original issue, and for the hard work on this LSP!