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/config.go

@@ -0,0 +1,43 @@
+package config
+
+import (
+	"os"
+
+	"gopkg.in/yaml.v3"
+)
+
+type DomainConfig struct {
+	TLD        string   `yaml:"tld"`
+	Subdomains []string `yaml:"subdomains"`
+}
+
+type Config struct {
+	ExternalIPProvider ExternalIpProviderConfig `yaml:"ip_provider"`
+	DNSProvider        DNSProviderConfig        `yaml:"dns_provider"`
+	Domains            []DomainConfig           `yaml:"domains"`
+	CheckInterval      string                   `yaml:"check_interval"`
+}
+
+type ExternalIpProviderConfig struct {
+	Type           string    `yaml:"type"`
+	ProviderConfig yaml.Node `yaml:"config"`
+}
+
+type DNSProviderConfig struct {
+	Type           string    `yaml:"type"`
+	ProviderConfig yaml.Node `yaml:"config"`
+}
+
+func (c *Config) Load(filePath string) error {
+	err := yaml.Unmarshal([]byte(filePath), c)
+	if err != nil {
+		inputConfig, err := os.ReadFile(filePath)
+		if err != nil {
+			return err
+		}
+
+		return yaml.Unmarshal(inputConfig, c)
+	}
+
+	return err
+}