Elastic Path Features API

A feature indicates some benefit that is received as a result of having an active subscription. This translates to tags being applied to the subscriber's account allowing access to some resource to be controlled.There are three types of feature - `access`, `promotion`, and `usage`.The `access` feature is designed to simply give access to some resource, for example a streaming service. If its tag is present on the subscriber's account then access to that resource should be provided.The `promotion` feature coupled with the [promotions service](/docs/promotions-builder/overview) allows subscribers to get access to a specific promotion. This is achieved using a tag which is used as a constraint on the promotion. A promotion feature may have multiple promotions associated with it, but just one must be selected when configuring the feature for an offering's plan. The `usage` feature is designed to measure some sort of usage of a resource. This currently relieson [commerce extensions](/docs/api/commerce-extensions/commerce-extensions-introduction) to manage usage. Once defined a feature may be attached to an offering, making it available for use with any of thatoffering's plans. Once attached it must be configured for each of the offering's plans it is applicable to. For the `promotion` feature this involves specifying which of that feature's tags, and hence which promotion, should be applied when subscribed to that offering. Similarly, for the `promotion` feature the default value for the usage metric must be supplied.