Add derivation for effective ozone temperature

[svniemeijer]

This is a quantity that is often used for ozone retrievals.

It is defined as: T_{eff} = integral(800hPa .. 10hPa, T(p)O3(p)dp) / integral(800hPa .. 10hPa, O3(p)dp)

See also the paper from Scarnato et al. from 2009.

We need to add:

• a variable name for this to the conventions in the document
• ingestion of ozone_effective_temperature field from S5P product
• a derivation to calculate this quantity from a pressure, temperature, and ozone profile

The derivation will need to cut off the vertical range of the profiles to 800hPa .. 10hPa. If this cut off reduces the remaining vertical range to less than x% of the 800hPa .. 10hPa profile range (e.g. because it lacks the troposphere or lacks the stratosphere part) we should return NaN. The value of x is TBD.