Update target platform on 8.3 for new Nuxeo distribution

See NXP-19643: the current package generated by Studio states a dependency to nuxeo-cap.

From 8.3, the nuxeo-cap dep should be considered for compatibility as nuxeo-server and JSF package marketplace-jsf-ui. Note that the same compat behaviour was introduced for nuxeo-dm migration to nuxeo-cap + DM package (see TARGET_PLATFORM#getMigratedTargetPlatform) so this can be taken as an example.

The JSF package will be marked as required for now (cannot be unchecked), this can be hardcoded for now: see additionnal tasks in NXS-3429 to allow unchecking it.

Target platform contributions for 8.3 and 8.4 need to be updated to remove nuxeo-cap and use nuxeo-server instead. There is no need splitting contributions coming from server and jsf-ui for now (this can wait for NXS-3429).