fix: re-add idp-initiated SSO (#1362)

## Overview
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* fixes removal of a capability we do actually support

## Type of change

**Type:** Fix incorrect doc removal

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## Additional notes
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Author: bvs-langchain

src/langsmith/self-host-sso.mdx

@@ -141,6 +141,7 @@ You must have administrator-level access to your organization's Google Cloud Pla
 
 #### Supported features
 
+* IdP-initiated SSO
 * SP-initiated SSO
 * Just-In-Time provisioning