fmuobs Warning when using ERROR_MODE != ABS

[alifbe]

ERT observation config is re-using ERROR keyword to store either absolute error value or relative error value (depending on ERROR_MODE)

However, the logic is not transferred when converting to ResInsight (csv) and probably Webviz (yml) which means if user specify 10% relative error in OBS config file. ResInsight will see it as 10 in absolute error value.

At this stage, trigger the warning when user is using ERROR_MODE that is no ABS.

The logic will be implemented in another PR.

[codecov-commenter]

Codecov Report

Merging #628 (08f57ef) into main (f761f64) will decrease coverage by 0.01%.
The diff coverage is 75.00%.

❗ Current head 08f57ef differs from pull request most recent head 4aa83c5. Consider uploading reports for the commit 4aa83c5 to get more accurate results

@@            Coverage Diff             @@
##             main     #628      +/-   ##
==========================================
- Coverage   84.00%   84.00%   -0.01%     
==========================================
  Files          52       52              
  Lines        7517     7521       +4     
==========================================
+ Hits         6315     6318       +3     
- Misses       1202     1203       +1     

Files	Coverage Δ
src/subscript/fmuobs/fmuobs.py	82.02% <75.00%> (-0.17%)	⬇️

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