[config] move config of the secret used to encrypt session's data ID in pyramid.ini (closes #11689082) Introduce a new config entry (in pyramid.ini) for this (cubicweb.session.secret) to replace the (now deprecated) pyramid-session-secret (in all-in-one.conf). So we have now 3 secrets to configure: - cubicweb.session.secret: to encrypt session's data ID stored in a cookie, - cubicweb.auth.authtkt.session.secret: to encrypt auth cookie - cubicweb.auth.authtkt.persistent.secret: to encrypt persistent session auth cookie

Document how to configure the "secure" flag for authentication policies Closes #11376233.

[tox] Let posargs override py.test args