Make use of cmake findBlas

[diego-plan9]

Description and motivation

It seems cmake offers a FindBLAS option directly, with some flags for determining which "vendor" to look for (BLA_VENDOR).

It would be worth looking into it, as potentially it could replace our need for FindAVX.cmake, FindOpenBLAS.cmake, FindMKL.cmake and some logic in dependencies.cmake (and allows us to redirect support about blas finding issues to cmake's).

Proposed solution

Replace the custom cmake files with a solution based on findBlas directly. A potentially time-consuming part is testing that the replacement works correctly in the usual environments and combinations.

Alternatives and other information