Improvement: make `control` optional within `userInterface` for all parameter types

[crowecawcaw]

The spec text for each parameter type (§2.1–2.4, §2.9+) already defines default values for control when it is not provided, but control lacks the @optional annotation. This means a user who only wants to set label or groupLabel is forced to redundantly specify control:

parameterDefinitions:
  - name: FrameCount
    type: INT
    userInterface:
      label: Frame Count

This should be valid since the default control is already defined, but implementations correctly reject it because the schema doesn't mark control as @optional.

Proposal

Add the @optional annotation to control within userInterface for all parameter types.

Reported by a user in aws-deadline/deadline-cloud#1109