Create measurement units

[rocketstack-matt]

Feature Request

Description of Problem:

#457 introduced time-unit which allows us to record a time in a control-requirement, but we need to be able to also record what it is we need to do in that period of time.

e.g.

    "throughput": {
      "type": "object",
       "properties": {
         "expected-message-rate": {
           "$ref": "https://calm.finos.org/draft/2024-10/meta/units.json#/defs/time-unit",
           "description": "Define the expected message rate that the flow should handle e.g. 1000 per second"
         }
       },
       "required": [
         "expected-message-rate"
       ]
     }

We state how long the thing must take e.g.

  "throughput": {
     "expected-message-rate": {
       "value": 1000,
       "unit": "seconds"
     }
   }

But we haven't set what needs to happen in the time, other than by a vague interpretation of the property.

Potential Solutions:

• Add a new definition which includes what it is that must happen (or be able to happen) in the time-unit and the value of that thing.
• Alternatively we could create a new standalone value def and include it alongside the time-unit.

My preference would be for a new specific def per the first option.