chore: review participants

Participants will be re-modeled as Invitations

openapi/components/schemas/participant.md

@@ -0,0 +1,4 @@
+
+Invitation to participate
+
+Poll participants are the actual users that participated.

openapi/components/schemas/participant.yaml

@@ -1,4 +1,6 @@
 type: object
+description:
+  $ref: 'participant.md'
 properties:
   id:
     readOnly: true

openapi/components/schemas/poll-properties.yaml

@@ -7,15 +7,6 @@ id:
     including some special characters like `_`.
   pattern: '[0-9a-fA-F_]{20}'
   example: 1jDe1e5eF_IkaYPuoIYX
-# uuid:
-#   readOnly: true
-#   type: string
-#   format: uuid
-#   # pattern is defined for implementations that don't understand format: uuid
-#   pattern: '[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}'
-#   description: >
-#     A Universally Unique IDentifier for the poll. (version 4)
-#   example: bb788552-727d-470b-827e-d7796248d293
 subject:
   type: string
   description: The subject of the poll.