docs: Document CUBEJS_DB_MIN_POOL (cube-js#10720)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: JLWalsh

docs/content/product/configuration/reference/environment-variables.mdx

@@ -664,6 +664,14 @@ The maximum number of concurrent database connections to pool.
 | --------------- | ------------------------------------------- | ------------------------------------------- |
 | A valid number  | [See database-specific page][ref-config-db] | [See database-specific page][ref-config-db] |
 
+## `CUBEJS_DB_MIN_POOL`
+
+The minimum number of database connections to pool.
+
+| Possible Values | Default in Development | Default in Production |
+| --------------- | ---------------------- | --------------------- |
+| A valid number  | `0`                    | `0`                   |
+
 ## `CUBEJS_DB_NAME`
 
 The name of the database to connect to.