[feature] Allow delivery to sharedInboxes where possible (#847)

* update Activity

* add instance-deliver-to-shared-inboxes setting

* update activity version again

* add SharedInboxURI field to accounts

* serdes for endpoints/sharedInbox

* deliver to sharedInbox if one is available

* update tests

* only assign shared inbox if shared domain

* look for shared inbox if currently nil

* go fmt

* finger to get params.RemoteAccountID if necessary

* make comments clearer

* compare dns more consistently

internal/ap/interfaces.go

@@ -40,6 +40,7 @@ type Accountable interface {
 	WithFollowers
 	WithFeatured
 	WithManuallyApprovesFollowers
+	WithEndpoints
 }
 
 // Statusable represents the minimum activitypub interface for representing a 'status'.
@@ -337,3 +338,8 @@ type WithItems interface {
 type WithManuallyApprovesFollowers interface {
 	GetActivityStreamsManuallyApprovesFollowers() vocab.ActivityStreamsManuallyApprovesFollowersProperty
 }
+
+// WithEndpoints represents a Person or profile with the endpoints property
+type WithEndpoints interface {
+	GetActivityStreamsEndpoints() vocab.ActivityStreamsEndpointsProperty
+}