feature: QuantityOrSensor fields for site capacities (flex-context)

[Flix6x]

Description

This PR updates the site-consumption-capacity and site-production-capacity fields in the flex-context to use the QuantityOrSensor schema.

Look & Feel

Example flex-context with a dynamic consumption capacity recorded under sensor ID 8:

{
    "flex-context": {
        "site-power-capacity": "500 kVA",
        "site-consumption-capacity": {"sensor": 8},
        "site-production-capacity": "400 kW",
    }
}

How to test

To do.

Further Improvements

• Write test
• CLI support
• Support site-power-capacity as a sensor? It's not as dynamic as it is usually related to cable thickness, but moreover I propose to wait until sensor support for the power-capacity field is fixed.
• Update endpoint documentation (in trigger_schedule docstring)
• Update API documentation (in scheduling.rst)
• Create Issue to create tutorial for modelling dynamic network capacity contracts Create tutorial for modelling dynamic network capacity contracts #999

Related Items

Closes #925.

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• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on code under GPL or other license that is incompatible with FlexMeasures

[victorgarcia98]

Great! This is something we are going to use a lot I think :D

I'm eager to see how to play with dynamic grid capacity constraints.

[victorgarcia98]

Awesome! Glad that you used the same test for the device production/consumption capacities.