Renames the release_enable_partners parameter to release_enable_partner_repack, and adds release_enable_partner_attribution for attribution. This it to provide support for disabling them independently in main releases, and in respins.
Adds docs for attribution, update docs for repacks.
Hardwire values for the enable params for the respin flavors, other wise read from the input (defaulting to on in promotion, off otherwise).
Fixes up the rebuild-kinds for partner repacks so that they reflect the current set, although the top level may be all that is needed.

Differential Revision: https://phabricator.services.mozilla.com/D87727