[RM-8235] set max number of candidates to retain after 1st pass to a dedicated parameter

Created on 2023-08-28 09:56:21 by Didier Vibert. % Done: 100

the maximum number of first pass candidate to retain is hardcoded to 5.
(see https://gitlab.lam.fr/CPF/cpf-redshift/-/blob/0.44-RC4/RedshiftLibrary/src/lib/method/linemodelsolve.cpp?ref_type=tags#L506 and https://gitlab.lam.fr/CPF/cpf-redshift/-/blob/0.44-RC4/RedshiftLibrary/src/lib/method/linemodelsolve.cpp?ref_type=tags#L552)

it should be a dedicated parameter eg linemodel.firstpass.extremacount
This has to be a distinct parameter than the global one linemodel.extremacount, since we may want to have a bigger number in first pass than in final, for instance if we retain only one solution for saving disk space.

Then in the parameters checking, this parameter has to be greater than the global one.