spp_farmer_registry: apply the registry-restriction rework from #411

[gonzalesedwin1123]

spp_farmer_registry carries its own copy of the registry-restriction implementation that #411 reworked in spp_starter_sp_mis: a registry_restriction.js controller patch plus the original config-parameter pattern.

#411 replaced that pattern for the starter module — explicit persistence for the setting (so "off" survives reloads and upgrades) and enforcement moved into a res.partner._check_access override, with the JS deleted. The same treatment should be ported here so both modules behave consistently.

Scope:

• Port the set_values/noupdate persistence fix for the farmer-registry setting
• Port the _check_access enforcement (scoped to registrants, admin exempt), including the is_registrant promotion guard from fix(starter_sp_mis): make registry access control persist and enforce #411's review
• Delete spp_farmer_registry/static/src/js/registry_restriction.js and its asset entry
• Port the fix(starter_sp_mis): make registry access control persist and enforce #411 test suite (test_registry_restriction.py) and adapt to this module's config parameter
• Whatever exemption mechanism lands from spp_starter_sp_mis: supported exemption from registry_admin_only_crud for designated non-admin roles #455 should apply to (or be shared with) this module — coordinate the two

Refs: #411 (starter rework), #455 (exemption follow-up).