Add the STORE module

This STORE module adds the following functionality:

- A function OSSL_STORE_open(), OSSL_STORE_load() and OSSL_STORE_close()
  that accesses a URI and helps loading the supported objects (PKEYs,
  CERTs and CRLs for the moment) from it.
- An opaque type OSSL_STORE_INFO that holds information on each loaded
  object.
- A few functions to retrieve desired data from a OSSL_STORE_INFO
  reference.
- Functions to register and unregister loaders for different URI
  schemes.  This enables dynamic addition of loaders from applications
  or from engines.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3542)