Validator proposals: confusing optional migrate message

[maurolacy]

The Create Validator proposal UI has a Migrate message field that is marked at optional. (Screenshot attached)

This message is not optional, and it's important not to miss it, because it's the json encoded migration message sent to the contract
during migration.

In any case, if the field has a default value of "empty" ({}), it would be better to state that ("default {}"), instead of the "optional" tag.