PURPOSE Provide some fixes after internal test deployment of event online features. Notably: user registration flow, various fixes in templates. Also add some unit tests to avoid regressions while working on event features. LINKS Task ID-2169118 odoo/odoo#55967 odoo/enterprise#12438 X-original-commit: e66684b23eebaadc3df7b908427d3d7a83d4f0a0