feat: Implement configuration management and DNS provider integration

- Added configuration management using Viper in internal/config/config.go
- Implemented ClientConfig, ServerConfig, TLSConfig, HetznerConfig, UpstreamConfig, and main Config struct.
- Created LoadConfig function to read and validate configuration files.
- Developed Hetzner DNS provider in internal/provider/hetzner/hetzner.go with methods for updating DNS records.
- Added comprehensive unit tests for configuration loading and Hetzner provider functionality.
- Established HTTP server with metrics and update endpoint in internal/server/server.go.
- Implemented request handling, authorization, and error management in the server.
- Created integration tests for the Hetzner provider API interactions.
- Removed legacy dynamic DNS integration tests in favor of the new API-based approach.

go.mod

@@ -0,0 +1,53 @@
+module git.cloonar.com/cloonar/updns
+
+go 1.22
+
+toolchain go1.23.7
+
+require (
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/bytedance/sonic v1.11.6 // indirect
+	github.com/bytedance/sonic/loader v0.1.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/cloudwego/base64x v0.1.4 // indirect
+	github.com/cloudwego/iasm v0.2.0 // indirect
+	github.com/fsnotify/fsnotify v1.8.0 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.3 // indirect
+	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/gin-gonic/gin v1.10.0 // indirect
+	github.com/go-playground/locales v0.14.1 // indirect
+	github.com/go-playground/universal-translator v0.18.1 // indirect
+	github.com/go-playground/validator/v10 v10.20.0 // indirect
+	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/goccy/go-json v0.10.2 // indirect
+	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.7 // indirect
+	github.com/leodido/go-urn v1.4.0 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
+	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.3 // indirect
+	github.com/prometheus/client_golang v1.22.0 // indirect
+	github.com/prometheus/client_model v0.6.1 // indirect
+	github.com/prometheus/common v0.62.0 // indirect
+	github.com/prometheus/procfs v0.15.1 // indirect
+	github.com/sagikazarmark/locafero v0.7.0 // indirect
+	github.com/sourcegraph/conc v0.3.0 // indirect
+	github.com/spf13/afero v1.12.0 // indirect
+	github.com/spf13/cast v1.7.1 // indirect
+	github.com/spf13/pflag v1.0.6 // indirect
+	github.com/spf13/viper v1.20.1 // indirect
+	github.com/subosito/gotenv v1.6.0 // indirect
+	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
+	github.com/ugorji/go/codec v1.2.12 // indirect
+	go.uber.org/multierr v1.10.0 // indirect
+	go.uber.org/zap v1.27.0 // indirect
+	golang.org/x/arch v0.8.0 // indirect
+	golang.org/x/crypto v0.32.0 // indirect
+	golang.org/x/net v0.33.0 // indirect
+	golang.org/x/sys v0.30.0 // indirect
+	golang.org/x/text v0.21.0 // indirect
+	google.golang.org/protobuf v1.36.5 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)