Migrates to Go modules, keeping updated vendor dir for compatibility.
This also moves "vendor/github.com/TykTechnologies/tykctl/api/_test_util/dash_mock.go" into the repo as "_test_util/dash_mock.go" since the original repo doesn't appear to exist, which causes issues when "tyk-k8s" is pulled in as a dependecy using Go modules.
Migrates to Go modules, keeping updated vendor dir for compatibility. This also moves "vendor/github.com/TykTechnologies/tykctl/api/_test_util/dash_mock.go" into the repo as "_test_util/dash_mock.go" since the original repo doesn't appear to exist, which causes issues when "tyk-k8s" is pulled in as a dependecy using Go modules.