chore: pass through new workflow executor config to LS

What does this MR do and why?

Passes through the new duo.workflow.executor config value to the Language Server.

This new config option will be used for selecting the new node executor. Valid config options are shell, docker, or the new node.

Note: this MR should not be merged until gitlab-org/editor-extensions/gitlab-lsp!1592 (merged) has been merged and the Language Server is updated in VSCode with that change included.

References

#1942 (closed)

Screenshots or screen recordings

n/a, no visual changes

How to set up and validate locally

See test instructions in the Language Server MR:

gitlab-org/editor-extensions/gitlab-lsp!1592 (merged)

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Closes #1942 (closed)