List webhooks with optional filters and pagination.

Query Parameters:

• page_size: Number of results per page (optional, default: 20, max: 50)
• cursor: Pagination cursor for next page (optional)
• filters: JSON-encoded WebhookFilters (optional)
  Example: ?filters={"status":"active","created_at_start":"2024-01-01"}

Returns a list of webhooks for the authenticated user. Privileged access
allows listing all webhooks for the account.