This adds doc/man7/OSSL_PROVIDER-default.pod and OSSL_PROVIDER-legacy.pod,
and fills in currently implemented operations and algorithms in them, as
well as in doc/man7/OSSL_PROVIDER-FIPS.pod, with links to documentation to
come.
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11270)