Add test for OSSL_PROVIDER_load with module path set

Add test for OSSL_PROVIDER_load with module path set

Ensure that, with the modulepath setting set in a config field, that we
are able to load a provider from the path relative to OPENSSL_MODULES

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24025)