Change addwebhook method to take an AddWebhookOpts param

[PaulSonOfLars]

What

AddWebhook() only uses one field in the WebhookOpts struct; this is confusing. Instead, move to using a new AddWebhookOpts struct

Impact

• Are your changes backwards compatible? N
• Have you included documentation, or updated existing documentation? Y
• Do errors and log messages provide enough context? Y