docs: update OSSL_PARAM_int documentation

docs: update OSSL_PARAM_int documentation

This change adds an example to allow compilation without warnings using
compiler options like `-Wincompatible-pointer-types-discards-qualifiers`

Code for the example was inspired by libarchive's https://github.com/libarchive/libarchive/pull/1869/commits/9e3a7e4b6c77e8aa19a69430f48917dbc15b319d

Fixes #20956

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27157)