This commit only adds the beta feature parameters and preference.
The API will need to check whether the feature is enabled.
The beta feature option is behind a feature flag
$wgEchoUseCrossWikiBetaFeature, that must be set to true for
the beta feature to appear on the wiki.
Bug: T114237
Change-Id: I61e1bd62571e55f7f685f64e0c37e7702875e407