rgw/sts: adding validation of jwks_uri cert according

rgw/sts: adding validation of jwks_uri cert according
to https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_providers_create_oidc_verify-thumbprint.html
for n&e which can be later used for all key types
(x5c, n&e).

Signed-off-by: Pritha Srivastava <prsrivas@redhat.com>
(cherry picked from commit d970f62e3e264644ea474ad4ee513caac977268f)

 Conflicts:
	src/rgw/rgw_rest_sts.cc
the conflict was due to validate_signature() taking thumbprints
in place of provider.thumbprints as input param.