Make prelimbe raise deprecation warning

[BSchilperoort]

Using --prelimbe will now raise the following warning:

WARNING:root:
  The years of the ERA5 preliminary back extension (1950 - 1978) are
  now included in the main ERA5 products. The `--prelimbe` argument
  will be deprecated in a future release.
  Please update your workflow accordingly.

The changelog has also been updated.

See #124

[codecov]

Codecov Report

Merging #147 (8aafeb9) into main (6e957b3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #147   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files          14       14           
  Lines         577      579    +2     
=======================================
+ Hits          575      577    +2     
  Misses          2        2           

[Peter9192]

Nice, that works