feat: Implement actor entity (#912)

This is a rewrite of #901, taking into account the clarified
requirements in #851

## Description

* Introduces the DialogActor entity, with DB migrations (breaking)
* Replaces the strings for "performedBy" and "seenBy" with instances of
DialogActor. This should also be used for "sender" when "transmission"
is introduced.
* Adds DTOs, mappings and validations for all enduser and service owner
endpoints
* Hash service replaced with static helper, used directly in mappers
* Refactored PersonNameRegistry to PartyNameRegistry
* Implement actor name lookup if actor id is supplied
* Replaced "via serviceowner" with a simple boolean value (should be
used in #386)
* Updated seen tests (pid masking)
* Added activity log tests (pid masking)

Missing
* Updated e2e tests

## Related Issue(s)

- #851

## Verification

- [x] **Your** code builds clean without any errors or warnings
- [x] Manual testing done (required)
- [ ] Relevant automated test added (if you find this hard, leave it and
we'll help out)

## Documentation

- [ ] Documentation is updated (either in `docs`-directory, Altinnpedia
or a separate linked PR in
[altinn-studio-docs.](https://github.com/Altinn/altinn-studio-docs), if
applicable)

---------

Co-authored-by: Ole Jørgen Skogstad <skogstad@softis.net>

docs/schema/V1/schema.verified.graphql

@@ -16,10 +16,16 @@ type Activity {
   extendedType: URL
   type: ActivityType!
   relatedActivityId: UUID
-  performedBy: String
+  performedBy: Actor!
   description: [Localization!]!
 }
 
+type Actor {
+  actorType: ActorType
+  actorId: String
+  actorName: String
+}
+
 type ApiAction {
   id: UUID!
   action: String!
@@ -173,8 +179,7 @@ type SearchDialogsPayload {
 type SeenLog {
   id: UUID!
   seenAt: DateTime!
-  endUserIdHash: String!
-  endUserName: String
+  seenBy: Actor!
   isCurrentEndUser: Boolean!
 }
 
@@ -224,6 +229,11 @@ enum ActivityType {
   FORWARDED
 }
 
+enum ActorType {
+  PARTY_REPRESENTATIVE
+  SERVICE_OWNER
+}
+
 enum ApplyPolicy {
   BEFORE_RESOLVER
   AFTER_RESOLVER