Databases: Update online migration docs (#973)

* Databases: Update online-migration docs

* add required and doc links

* misspell

specification/resources/databases/databases_update_onlineMigration.yml

@@ -6,8 +6,9 @@ description: >-
   To start an online migration, send a PUT request to
   `/v2/databases/$DATABASE_ID/online-migration` endpoint. Migrating a cluster
   establishes a connection with an existing cluster and replicates its
-  contents to the target cluster. Online migration is only available for
-  MySQL, PostgreSQL, and Redis clusters.
+  contents to the target cluster. If the existing database is continuously being written to, 
+  the migration process will continue for up to two weeks unless it is manually stopped. Online migration is only available for
+  [MySQL](https://docs.digitalocean.com/products/databases/mysql/how-to/migrate/#:~:text=To%20migrate%20a%20MySQL%20database,then%20select%20Set%20Up%20Migration), [PostgreSQL](https://docs.digitalocean.com/products/databases/postgresql/how-to/migrate/), and [Redis](https://docs.digitalocean.com/products/databases/redis/how-to/migrate/) clusters. 
 
 tags:
   - Databases

specification/resources/databases/models/online_migration.yml

@@ -10,6 +10,7 @@ properties:
     description: The current status of the migration.
     enum:
       - running
+      - syncing
       - canceled
       - error
       - done

specification/resources/databases/models/source_database.yml

@@ -1,5 +1,8 @@
 type: object
 
+required:
+  - source
+
 properties:
   source:
     type: object