Hide feature toggles from the next.gitter.im UI

Hide feature toggles from the next.gitter.im UI

MR for next.gitter.im: https://gitlab.com/gitlab-org/gitter/next-gitter-im/merge_requests/2

Sometimes we just want to control the feature toggle ourselves.

Spawned from the left-menu and new vue-left-menu feature toggle which can cause confusion so just opting to hide the left-menu feature toggle.

You can still toggle these via the API, they just aren't listed on next.gitter.im

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node ./scripts/utils/feature-toggle.js --name test-hidden-feature --description "Testing hidden feature toggles" --hidden