API addition in events payload

[bkircher]

GET /objects/servers//events as well as GET /objects/events and all other events end-points now include an additional key "initiator" whose value is a string.

From the docs, initiator is "The user that triggered the event. Usually the user's email if the event was triggered by request of a user, otherwise a short descriptive name of the system component responsible."

Docs here: https://gridscale.io/en/api-documentation/index.html#operation/getServerEvents

Please add this to EventProperties struct.