docs(api): add webhooks link to API overview (#1739)

Adds a link to the [Webhooks](/admin/webhooks/) docs from the [API
overview page](/api/), alongside the other integration-specific API
links.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: bobheadxi

docs/api/index.mdx

@@ -14,6 +14,7 @@ For specific types of integrations, Sourcegraph also offers the following APIs:
 - [Sourcegraph streaming search API](/api/stream-api/), for consuming search results as a stream of events
 - [Sourcegraph MCP server](/api/mcp/), for connecting AI agents and applications to Sourcegraph's code search capabilities
 - [Sourcegraph Analytics API](/analytics/api/), for accessing your Sourcegraph Analytics data
+- [Webhooks](/admin/webhooks/), for receiving event notifications from Sourcegraph
 
 For diagnostics use cases, the [Sourcegraph GraphQL debug API](/api/graphql/) is also available without any compatibility guarauntees.