Migrate GenKW template feature into global template option (substitutions)

[xjules]

Currently each GEN_KW keyword allows to setup a template feature (using template and output file). We should still parse those options, but instead migrate the actual templating into the global substitutions when creating run_path essentially here:

ert/src/ert/enkf_main.py

Line 245 in c5be0c7

for source_file, target_file in templates:

This will require to propagate ScalarParameter(s) into the substitutions dict (key:value).
This should be based on #10095