Add webhook structs and methods (#10)

Signed-off-by: Raphaël Pinson <[email protected]>

go.mod

@@ -5,11 +5,17 @@ go 1.23
 require (
 	github.com/shurcooL/graphql v0.0.0-20230722043721-ed46e5a46466
 	github.com/stretchr/testify v1.9.0
+	github.com/svix/svix-webhooks v1.38.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/golang/protobuf v1.5.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/stretchr/objx v0.5.2 // indirect
+	golang.org/x/net v0.23.0 // indirect
+	golang.org/x/oauth2 v0.0.0-20210514164344-f6687ab2804c // indirect
+	google.golang.org/appengine v1.6.6 // indirect
+	google.golang.org/protobuf v1.33.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )