Pre-PR: webhook creation support about go-onfido

[MarkSonghurst]

@cpick If you want I can submit my files as a PR. It's your code though so I don't want to take the glory ;-)

[MarkSonghurst]

@cpick Many thanks for your work, I need to list webhooks so I copied your diff into my own fork and also added unit tests.
I made some minor changes to suit my Go coding style, such as creating a new source file for your code.
It's all cosmetic stuff.
I've since abandoned making PRs into this parent fork, but if you want my changes you can find them here:
https://github.com/MarkSonghurst/go-onfido/blob/webhook/webhookref.go
https://github.com/MarkSonghurst/go-onfido/blob/webhook/webhookref_test.go

Thanks again, you saved me a days work :-)

[SpeedyCoder]

@cpick this looks good, we would be happy to add it to this repo. I can't think of any better name than WebhookRef . Though I would prefer to have things in separate files like @MarkSonghurst did on his branch, as interacting with the webhook api and parsing webhook calls are two quite different things.

Sorry for being super slow to respond, I was busy with other stuff and forgot about the PRs and issues on this repo 😅 I have now cleaned up most of the pending PRs and I will try to be more responsive from now on.

[cpick]

@MarkSonghurst that would be great, please do!

[SpeedyCoder]

This was added in #25