Copilot extension

Add a copilot extension to assist VSCode users in the feature flag lifecycle.

The usefulness of this will likely depend on the implementation of more flag lifecycle functionality so that we can help with removing stale flags, etc.

That being said, just having the ability to create a flag and wrap some block of code in it might be helpful.

See details of LD's implementation [here](https://docs.launchdarkly.com/integrations/github-copilot-extension).