Automatic HTTP Strict Transport Security enforcing for [class@Session].
A [class@HSTSEnforcer] stores HSTS policies and enforces them when required. [class@HSTSEnforcer] implements [iface@SessionFeature], so you can add an HSTS enforcer to a session with [method@Session.add_feature] or [method@Session.add_feature_by_type].
[class@HSTSEnforcer] keeps track of all the HTTPS destinations that, when connected to, return the Strict-Transport-Security header with valid values. [class@HSTSEnforcer] will forget those destinations upon expiry or when the server requests it.
When the [class@Session] the [class@HSTSEnforcer] is attached to queues or restarts a message, the [class@HSTSEnforcer] will rewrite the URI to HTTPS if the destination is a known HSTS host and is contacted over an insecure transport protocol (HTTP). Users of [ class@HSTSEnforcer] are advised to listen to changes in the [property@Message:uri] property in order to be aware of changes in the message URI.
Note that [class@HSTSEnforcer] does not support any form of long-term HSTS policy persistence. See [class@HSTSEnforcerDB] for a persistent enforcer.