fix: Provide MKL Paths with MKLConfig.cmake

[hollowsunhc]

This Pull Request leverages the use of MKLConfig.cmake in the context where we do want to provide an external Intel MKL

Additionally, projects using SuiteSparse will be able to set the same provided Intel MKL.

To test this PR, the following CMake variables must be set:

• "WITH_MKL": "ON"
• "MKL_DIR": "your/path/to/mkl/lib/cmake/mkl/"
• "HUNTER_ENABLED": "OFF"

ENV{MKLROOT} must resolve in order to correctly find BLAS libraries (add MKLROOT to environment variables)

[hollowsunhc]

Hmm there's still an issue with this PR....

In SuiteSparse-targets.cmake, INTERFACE_LINK_LIBRARIES of targets like SuiteSparse::spqr contain absolute paths of MKL library files when it should simply be MKL::MKL

I guess this remaining problem stems from the fact that we're not passing MKL::MKL but instead passing MKL libraries using get_property(BLAS_LIBRARIES TARGET MKL::MKL PROPERTY INTERFACE_LINK_LIBRARIES)