Letsencrypt allows using a specific key type for certificates. If the user has an internal letsencrypt mechanism, such as Vault Acme, then they have to provide a specific key type as the default is not supported. This change will allow a user to specify a key type and use the lego default in the event that they don't specify it. Partial-Bug: 2087860 Change-Id: I83e618a861b4d51b6a7893f79c50fdfc35228891