feat: mvp (#1)

MVP including features:
* Detect IP change
* Configurable/generic external IP provider
* Configurable/generic DNS provider
* Impl. of plain external IP provider
* Impl. of Ionos DNS provider

Reviewed-on: #1
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

go.mod

@@ -0,0 +1,15 @@
+module realdnydns
+
+go 1.20
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/go-co-op/gocron v1.31.2 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/robfig/cron/v3 v3.0.1 // indirect
+	github.com/stretchr/objx v0.5.0 // indirect
+	github.com/stretchr/testify v1.8.4 // indirect
+	go.uber.org/atomic v1.9.0 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)