[IMP] website: add templates for footer

Also remove all t-fields from footers to have only static contents in
footers. For social links, a controller is added so that a "static url"
/website/social/xxx always redirect to the correct set URL for the given
xxx social network.

Part of https://github.com/odoo/odoo/pull/38950


task-2087641

Co-authored-by: qsm-odoo <qsm@odoo.com>