Introduce the newly chosen standard name

As we have discussed in https://github.com/orgs/cf-convention/discussions/429, to be accurate, Satpy should not name quantities not normalised with the sun zenith angle as "toa_bidirectional_reflectance".

We thus need to introduce a new standard name in satpy for these quantities.
It might take while to get an official standard name in the cf conventions, so for now we are going to go for "oblique_toa_bidirectional_reflectance" "product_of_cosine_solar_zenith_angle_and_toa_bidirectional_reflectance", and use that until an official standard name is adopted.

Here are some of the to-do items we have identified so far.

• Decide on something to use for now
• Update base reader class to overwrite standard_name if “sunz_corrected” modifier is not present
• Update enhancer to detect old standard name being matched and absence of “sunz_corrected” modifier and produce warning
• Add satpy.config feature flag for pseudo-reflectance standard name to be False by default in 0.60, True in 1.0.
• Copy all existing “toa_bidirectional_reflectance” enhancements with the new standard name for pseudo-reflectance since they are used interchangeably right now

Start with the linked discussion to resolve the temporary standard name, then inspect the base reader class, enhancer, satpy.config feature flag, and existing toa_bidirectional_reflectance enhancements. Done means pseudo-reflectance uses the chosen name, the old-name case warns appropriately, the flag has the requested defaults, and equivalent enhancements exist.