feat: add version downgrade for live-migration FAQ

[Harkishen-Singh]

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.

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[github-actions]

Allow 10 minutes from last push for the staging site to build. If the link doesn't work, try using incognito mode instead. For internal reviewers, check web-documentation repo actions for staging build status. Link to build for this PR: http://docs-dev.timescale.com/docs-hs-more-live-migration-faq

[billy-the-fish]

Suggested change

	## Source database does not have the latest TimescaleDB version
	Live migration requires the TimescaleDB version in the source database to be the same as
	that in the target database (Timescale Cloud). However, in certain instances, the TimescaleDB
	version installed in the target database may differ from that available in the source
	database, such as in the case of Managed Service for TimescaleDB. In such scenarios,
	instead of upgrading the source database, an alternative approach is to downgrade the
	TimescaleDB version in the target database to align it with the version available in
	the source database.
	This can be achieved by first uninstalling the TimescaleDB extension from the
	target database using the following command:
	```sql
	DROP EXTENSION timescaledb;
	```
	Then, reinstall TimescaleDB extension with the desired version:
	```sql
	CREATE EXTENSION timescaledb VERSION '<version>';
	```
	<Highlight type="note">
	You might need to reconnect `psql` with the `-X` flag to prevent reading the startup file.
	</Highlight>
	To determine which TimescaleDB versions are available on Timescale Cloud and can
	be used for the downgrade, execute the following query:
	```sql
	SELECT version FROM pg_available_extension_versions WHERE name = 'timescaledb' ORDER BY 1 DESC;
	```
	## Source database is not running the latest version of TimescaleDB
	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]:
	<Procedure >
	1. Check the version of TimescaleDB running on the source database and the
	target Timescale Service:
	```sql
	\dx timescaledb
	```
	You see the following:
	```sql
	Name | Version | Schema | Description
	-------------+---------+------------+---------------------------------------------------------------------
	timescaledb | x.y.z | public | Enables scalable inserts and complex queries for time-series data
	(1 row)
	```
	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">
	To prevent reading the startup file, reconnect to your Timescale Service using `psql -X` .
	</Highlight>
	- **Upgrade**: for self-hosted databases,
	[upgrade TimescaleDB][self hosted upgrade] to match your Timescale Service.
	</ Procedure>
	[live migration]: /migrate/:currentVersion:/live-migration/
	[self hosted]: /self-hosted/:currentVersion:/
	[self hosted upgrade]: /self-hosted/:currentVersion:/upgrades/
	[mst]: /managed/:currentVersion:/
	[timescale-service]: https://console.cloud.timescale.com/dashboard/services

[Harkishen-Singh]

@billy-the-fish thanks for the suggestions. I have implemented the changes.

[billy-the-fish]

Hi, hope you are ok with the changes I propose.

[billy-the-fish]

LGTM