VSCE: Update CTA banner and add dismiss button
Created by: abeatrix
This PR updates the CTA banner with the one from web app ({ CtaAlert } from '@sourcegraph/shared/src/components/CtaAlert'
) and add dismiss button to the banner that is persistent (store in vs code storage):
Close: https://github.com/sourcegraph/sourcegraph/issues/31089
Test plan
Currently N/A for VSCE