Add an optional API worker for [AlientVault's OTX](https://otx.alienvault.com/). ### Example Usage * https://github.com/hueristiq/xurlfind3r/blob/2a369c4b050e6018a36a69146f76ad22fbd3683b/pkg/xurlfind3r/sources/otx/otx.go#L85-L144
