Fix DDNS bugs and split up ddns module (#326)

* fix: webhook retry logic
fix: adjust record type based on ipv4 ipv6
refract: move ddns providers to a new module

* refract: move ddns module to pkg/

pkg/ddns/dummy.go

@@ -0,0 +1,7 @@
+package ddns
+
+type ProviderDummy struct{}
+
+func (provider ProviderDummy) UpdateDomain(domainConfig *DomainConfig) bool {
+	return false
+}