Add experimental feature flag for home panels compute suggestions

Created by: limitedmage

A feature flag is needed for the home panels suggestions project.

• The name of this feature flag could be homePanelsComputeSuggestions (if you have a better name feel free to use it :) )
• The feature flag needs to be added to https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/schema/settings.schema.json under experimentalFeatures
• Once the schema is updated (run yarn generate and go generate ./...), you can use the feature flag with the hook useExperimentalFeature. See example use.