feat: add version downgrade for live-migration FAQ (#3163)

Signed-off-by: Harkishen-Singh <harkishensingh@hotmail.com>

This commit adds a FAQ question that helps users to downgrade
TimescaleDB version on their target database to match with the
source database. This is useful when the source database (MST) does not
have the TimescaleDB version that the target database is installed
with.

migrate/live-migration/live-migration-faq.md

@@ -19,6 +19,56 @@ the migration. The logs of these processes can be helpful for troubleshooting
 unexpected behavior. You can find these logs in the `<volume_mount>/logs` directory.
 
 
+## Source and target databases have different TimescaleDB versions
+
+When you migrate a [self-hosted][self hosted] or [Managed Service for TimescaleDB (MST)][mst]
+database to Timescale, the source database and the destination
+[Timescale Service][timescale-service] must run the same version of TimescaleDB.
+
+Before you start [live migration][live migration]:
+
+
+1. Check the version of TimescaleDB running on the source database and the
+   target Timescale Service:
+    ```sql
+    select extversion from pg_extension where extname = 'timescaledb';
+    ```
+
+1. If the version of TimescaleDB on the source database is lower than your Timescale Service, either:
+   - **Downgrade**: reinstall an older version of TimescaleDB on your Timescale
+      Service that matches the source database:
+
+     1. Connect to your Timescale Service and check the versions of TimescaleDB available:
+        ```sql
+        SELECT version FROM pg_available_extension_versions WHERE name = 'timescaledb' ORDER BY 1 DESC;
+        ```
+
+     2. If an available TimescaleDB release matches your source database:
+
+        1. Uninstall TimescaleDB from your Timescale Service:
+           ```sql
+           DROP EXTENSION timescaledb;
+           ```
+
+        1. Reinstall the correct version of TimescaleDB:
+           ```sql
+           CREATE EXTENSION timescaledb VERSION '<version>';
+           ```
+
+        <Highlight type="note">
+        You may need to reconnect to your Timescale Service using `psql -X` when you're creating the TimescaleDB extension.
+        </Highlight>
+
+   - **Upgrade**: for self-hosted databases,
+     [upgrade TimescaleDB][self hosted upgrade] to match your Timescale Service.
+
+[live migration]: /migrate/:currentVersion:/live-migration/
+[self hosted]: /self-hosted/:currentVersion:/
+[self hosted upgrade]: /self-hosted/:currentVersion:/upgrades/
+[mst]: /mst/:currentVersion:/
+[timescale-service]: https://console.cloud.timescale.com/dashboard/services
+
+
 ## Why does live migration log "no tuple identifier" warning?
 
 Live migration logs a warning `WARNING: no tuple identifier for UPDATE in table`