Webhook resource exposes secrets on preview

[IaroslavTitov]

What happened?

Whenever a secret is passed into Webhook's secret property, it is not covered up with [secret during] preview.

Example

Create a webhook resource, with secret passed into secret field.
Run pulumi up, then select details.
Value is exposed.

Output of pulumi about

Not relevant

Additional context

No response

Contributing

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[IaroslavTitov]

Fixed in #370