Add changelog for 2025-06-07-1 (#536)

Author: quantstruct-bot

fern/changelog/2025-06-25-1.mdx

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+<Card title="Support Ticket Submission via API" icon="ticket" href="https://api.vapi.ai/api#:~:text=SupportTicket">
+  **Create support tickets directly through Vapi ** using the new [`/support/ticket`](https://api.vapi.ai/api#:~:text=SupportTicket) endpoint, simplifying how you request assistance.
+</Card>
+
+**HMAC Authentication for Webhook Credentials**: Secure your webhooks with HMAC authentication by configuring [`Assistant.credentials.authenticationPlan`](https://api.vapi.ai/api#:~:text=Assistant,-AssistantPaginatedResponse) with [`HMACAuthenticationPlan`](https://api.vapi.ai/api#:~:text=HMACAuthenticationPlan), providing an alternative to OAuth2.
+
+<Warning>
+  **Deprecation Notice**: The `concurrencyLimit` setting in organization configurations is now deprecated.
+</Warning>
+