Feature/merge time series schemas

[Flix6x]

Description

• Merge two core schemata used to specify time series data in a flex model, namely QuantityOrSensor and TimeSeriesOrSensor.
• Named new schema VariableQuantityField.
• Backward compatibility: deprecate old schemas, but keep them functioning for now (while logging a deprecation warning).
• Allow setting a SoC unit directly in some fields (formerly Float fields, and now Quantity fields), while still falling back on the contents of the soc-unit field, for backwards compatibility:
  • soc-at-start
  • soc-min
  • soc-max
• Allow setting a unit directly in fields that already supported passing a time series:
  • soc-maxima
  • soc-minima
  • soc-targets
• Allow passing a time series in fields that formerly only accepted passing a fixed quantity or a sensor reference:
  • power-capacity
  • consumption-capacity
  • production-capacity
  • charging-efficiency
  • discharging-efficiency
  • storage-efficiency
  • soc-gain
  • soc-usage
• Revise docs in flex-model-v2g.rst with regards to passing dynamic power constraints as part of the flex-model
• Remove all but one mention of the soc-unit field from the docs (still works under the hood)
• Add test cases for passing a time series to the new schema

Look & Feel

Synchronizes support for specifying time series data in a flex model in three distinct ways:

• As a constant quantity, such as:

  "10 kW"
  

• As a time series, such as (NB the below example assumes the unit is specified via a separate field):

  [
      {
          "value": 51,
          "start": "2024-02-04T10:35:00+01:00",
          "end": "2024-02-05T04:25:00+01:00"
      }
  ]
  

• As a sensor, such as:

  {
      "sensor": 101
  }
  

How to test

See https://github.com/FlexMeasures/flexmeasures/pull/1127/files#diff-1f68bebf4090d2608b43200311d3ebd3e0ad637e2e16cc6a9b14bffaa29757f3R2177

Further Improvements

• Documentation update regarding variable quantity fields moved to Docs/update section on API field notation #1138.
• Documentation update regarding scheduling in different units moved to Redo the toy tutorial for scheduling a battery with kW and kWh units #1139.

Related Items

• Closes Schedule non-MW sensors #386.
• Closes Send dynamic powerconstraint in flex-model #1109.

[nhoening]

In #1128 we also mentioned that:

• we'd close Schedule non-MW sensors #386
• we'd add examples (of scheduling non-MW sensors) to the documentation

If this PR is the successor, then it should also take those promises over. They might be rather meaningful for users.

[Flix6x]

• we'd add examples (of scheduling non-MW sensors) to the documentation

Moved to #1139

[victorgarcia98]

Thanks!