step-ca: Allow longer validity for ACME certificates

By default, step-ca issues certificates that are valid for only one day.
This means that clients need to have multiple renew attempts scheduled
throughout the day, otherwise, missing one could mean having their
certificates expire.  This is unnecessary, and not even possible in all
cases, so let's make the default validity period longer and avoid the
issue.

step-ca/ca.json

@@ -25,7 +25,11 @@
 		"provisioners": [
 			{
 				"type": "ACME",
-				"name": "acme"
+				"name": "acme",
+				"claims": {
+					"maxTLSCertDuration": "744h",
+					"defaultTLSCertDuration": "168h"
+				}
 			},
 			{
 				"type": "OIDC",