Migrate mdatagen tool from using yaml to koanf/mapstructure (#6460)

For consistency with other parts of the project

cmd/mdatagen/go.mod

@@ -7,15 +7,29 @@ require (
 	github.com/go-playground/universal-translator v0.18.0
 	github.com/go-playground/validator/v10 v10.9.0
 	github.com/stretchr/testify v1.7.0
-	gopkg.in/yaml.v2 v2.4.0
+	go.opentelemetry.io/collector v0.40.0
 )
 
 require (
+	github.com/benbjohnson/clock v1.2.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/fsnotify/fsnotify v1.4.9 // indirect
+	github.com/knadh/koanf v1.3.2 // indirect
 	github.com/leodido/go-urn v1.2.1 // indirect
+	github.com/magiconair/properties v1.8.5 // indirect
+	github.com/mitchellh/copystructure v1.2.0 // indirect
+	github.com/mitchellh/mapstructure v1.4.2 // indirect
+	github.com/mitchellh/reflectwalk v1.0.2 // indirect
+	github.com/pelletier/go-toml v1.9.3 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/spf13/cast v1.4.1 // indirect
+	go.uber.org/atomic v1.9.0 // indirect
+	go.uber.org/multierr v1.7.0 // indirect
+	go.uber.org/zap v1.19.1 // indirect
 	golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97 // indirect
-	golang.org/x/sys v0.0.0-20210806184541-e5e7981a1069 // indirect
+	golang.org/x/sys v0.0.0-20211013075003-97ac67df715c // indirect
 	golang.org/x/text v0.3.6 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )