Added CustomerFirstNameSet, CustomerLastNameSet, and CustomerTitleSet Messages

With the addition of three new Messages you can now use the MessageSubscription to subscribe to changes on the firstName, lastName, and title fields on Customers specifically. Before, you had to use the generic ChangeSubscription for that. These Messages are triggered by Set First Name, Set Last Name, and Set Title update actions.

Changes:

• [API] Added CustomerFirstNameSetMessage.
• [API] Added CustomerLastNameSetMessage.
• [API] Added CustomerTitleSetMessage.
• [GraphQL API] Added the following types to the GraphQL schema: CustomerFirstNameSet, CustomerLastNameSet, CustomerTitleSet.

The following changes were introduced in terms of GraphQL SDL:

type CustomerFirstNameSet implements MessagePayload {
  firstName: String
  type: String!
}

type CustomerLastNameSet implements MessagePayload {
  lastName: String
  type: String!
}

type CustomerTitleSet implements MessagePayload {
  title: String
  type: String!
}