STEPS blending procedure with other nowcasting models

[RubenImhoff]

The current STEPS blending procedure implicitly uses the STEPS nowcasting procedure, but in principle, a similar approach should also be possible with other conventional and machine-learning nowcasting models. We could think of an additional blending script that is adapted from ./blending/steps.py which takes an existing nowcast as input instead of the individual radar images.

Tasks:

• Finalization of issue STEPS blending approach with deterministic external nowcast #499.
• Ensemble setup for blending external nowcast with NWP.
• Add tests.
• Gallery example.

[RubenImhoff]

@Joep1999 (couldn't assign it to you for some reason, but herewith the issue).