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>

pkg/config/__mocks__/testLoadCanFindFile.yaml

@@ -0,0 +1,16 @@
+---
+ip_provider:
+  type: plain
+  config:
+    url: https://ifconfig.me
+dns_provider:
+  type: ionos
+  config:
+    api_key: exampleAPIKey
+    base_url: https://example.com
+domains:
+  - tld: example.com
+    subdomains:
+      - "@"
+      - www
+check_interval: 0 0 0/6 * * * *