Related: https://core.trac.wordpress.org/ticket/64837#ticket

When WP_ENVIRONMENT_TYPE is local, development, or staging, webmentions should be disabled.

Unless one remembers to go in and disable webmentions on a non-production environment, mentions will be sent out when posts are added or updated, which is a common workflow when testing. This is not ideal and creates confusion on the receiving end. Disabling them on non-production environments default would be a better experience.

• Both outgoing and incoming should be disabled.
• If the environment type is not set, or is set to production, webmentions should be left as default (open/enabled).
• A filter should be added so developers can override this change if webmentions are needed in a non-production environment.