Test genpkey app for EC keygen with various args

Test genpkey app for EC keygen with various args

This commit adds a new recipe to test EC key generation with the
`genpkey` CLI app.

For each built-in curve, it tests key generation with text output, in
PEM and in DER format, using `explicit` and `named_curve` for parameters
encoding.

The list of built-in curves is static at the moment, as this allows to
differentiate between prime curves and binary curves to avoid failing
when ec2m is disabled.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12080)