Add type property to custom granularities documentation

Generated-By: mintlify-agent

Author: mintlify[bot]

references/lightdash-config-yml.mdx

@@ -264,12 +264,15 @@ custom_granularities:
   fiscal_quarter:
     label: "Fiscal Quarter"
     sql: "DATE_TRUNC('quarter', ${COLUMN} + INTERVAL '1 month')"
+    type: date
   week_monday:
     label: "Week (Mon-Sun)"
     sql: "DATE_TRUNC('week', ${COLUMN})"
+    type: date
   fiscal_year:
     label: "Fiscal Year"
     sql: "EXTRACT(YEAR FROM ${COLUMN} + INTERVAL '1 month')"
+    type: string
 ```
 
 Each custom granularity is defined as a key-value pair where the key is the granularity name (must be alphanumeric with underscores) and the value is an object with the following properties:
@@ -278,6 +281,7 @@ Each custom granularity is defined as a key-value pair where the key is the gran
 | :------- | :------- | :----- | :---------- |
 | `label`  | Yes      | string | A user-friendly label for the granularity as it will be displayed in the date zoom dropdown. |
 | `sql`    | Yes      | string | SQL expression that defines how to truncate/transform the date. Use `${COLUMN}` as a placeholder for the actual date column - it will be replaced with the column's SQL at runtime. |
+| `type`   | No       | `date`, `timestamp`, or `string` | The output type of the SQL expression. Use `date` for truncated dates, `timestamp` for truncated timestamps, or `string` for formatted text output (e.g., fiscal year labels). Defaults to `date` if not specified. |
 
 ### How custom granularities work
 
@@ -291,6 +295,7 @@ custom_granularities:
   fiscal_quarter:
     label: "Fiscal Quarter"
     sql: "DATE_TRUNC('quarter', ${COLUMN} + INTERVAL '1 month')"
+    type: date
 ```
 
 ```yaml