Upgrade proto2 to proto3 in the statemachine

[xjules]

The current state machine exploits functionality of protobuffer proto2 (see https://github.com/equinor/ert/blob/58670dd7149b917685dac96f86da9923fa751302/src/ert/com_protocol/_schema.proto), which allows us to inject defaults when creating the DispatcherMessage. Neverthelles it is recommended to upgrade to proto3, which would allow for more control of the values and also would support better linting. For example nested enums produce (no-member) linting error.