Add Snowflake per-user OAuth docs

[mustafa3rsan]

No description provided.

[greptile-apps]

Security Review

The setup guide should explicitly warn that disabling Snowflake's privileged-role OAuth safeguard is account-wide and affects integrations beyond Bruin.

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### Issue 1
docs/cloud/ai-agents/snowflake-oauth.md:86
**Account-wide OAuth safeguard removal**

This alternative disables privileged-role blocking for every OAuth security integration in the Snowflake account, not only `bruin_oauth`. State that account-wide impact explicitly and recommend switching to a non-privileged default role so administrators do not unintentionally broaden high-privilege OAuth access.

**How this was verified:** The documented command alters an account-level parameter rather than the Bruin security integration.

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "Add Snowflake per-user OAuth docs, keep ..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (2): Last reviewed commit: "docs(snowflake-oauth): drop unverified O..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (3): Last reviewed commit: "Leave pkg/snowflake/config.go untouched ..." | Re-trigger Greptile}