Snowflake source freshness (#5228)

## What are you changing in this pull request and why?

Closes #4876

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Co-authored-by: Leona B. Campbell <[email protected]>

website/docs/docs/deploy/source-freshness.md

@@ -41,4 +41,5 @@ It's important that your freshness jobs run frequently enough to snapshot data l
 
 ## Further reading
 
-Refer to [Artifacts](/docs/deploy/artifacts) for more info on how to create dbt Cloud artifacts, share links to the latest documentation, and share source freshness reports with your team.
+- Refer to [Artifacts](/docs/deploy/artifacts) for more info on how to create dbt Cloud artifacts, share links to the latest documentation, and share source freshness reports with your team.
+- Source freshness for Snowflake is calculated using the `LAST_ALTERED` column. Read about the limitations in [Snowflake configs](/reference/resource-configs/snowflake-configs#source-freshness-known-limitation).

website/docs/reference/resource-configs/snowflake-configs.md

@@ -479,3 +479,15 @@ The workaround is to execute `DROP TABLE my_model` on the data warehouse before
 </VersionBlock>
 
 </VersionBlock>
+
+
+## Source freshness known limitation
+
+Snowflake calculates source freshness using information from the `LAST_ALTERED` column, meaning it relies on a field updated whenever any object undergoes modification, not only data updates. No action must be taken, but analytics teams should note this caveat. 
+
+Per the [Snowflake documentation](https://docs.snowflake.com/en/sql-reference/info-schema/tables#usage-notes): 
+
+  >The `LAST_ALTERED` column is updated when the following operations are performed on an object:
+  >- DDL operations.
+  >- DML operations (for tables only).
+  >- Background maintenance operations on metadata performed by Snowflake.