Increase default key size for CA to 3072 bits
    
    The signing key for IPA's CA certificate now uses a 3072 bit RSA key by
    default.
    
    According to https://www.keylength.com/, NIST 800-57 Part 1 Rev. 4
    recommends 3072 bit RSA keys for keys that are used beyond 2030 for 128 bit
    strength.
    
    Fixes: https://pagure.io/freeipa/issue/6790
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>