Feels like temperature

### What problem does your feature request solve?

The temperature that is quoted in the forecasts is the dry-bulb measured under shade. Fundamentally though the public are really interested in what the temperature "feels-like". In winter the temperature is more controlled by the "wind chill" factor (wind), whereas in summer the temperature is more controlled by the "heat index" (i.e. humidity). Average temperatures use a combination of both the wind chill factor and the heat index to find the "feels-like" temperature.

### Describe the solution you'd like

A new operator is required that will calculate the feels like temperature, and be dependent upon whether it is above or below average use the relevant factors. This should live under `Daily Weather`.

These diagnostics should only use model output and not ancillary data. Any method ancillary data should ideally occur within the model.

For further details (including about reviewers) please refer to #1550.

### Required diagnostics

Temperature at screen level
Windspeed at 10 m
Relative humidity at screen level

Start with the Daily Weather operator area and read issue #1550 for the referenced details and reviewers. Confirm how model-output diagnostics expose screen-level temperature, 10 m windspeed, and screen-level relative humidity; done means a feels-like operator is added there using those diagnostics.

Written by the indexing model from the issue text.