[Change] MST Extension upgrade instructions should inform adding -X flag before the upgrade command is executed.

[hardikm10]

Change in content, appearance, or functionality?
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Describe the change
The command only mentions "alter extension timecaledb update" but it doesn't mention that
a) using psql and -X flag to connect first
b) it should be the first command you need to execute

Similar to how we already mention at https://docs.timescale.com/self-hosted/latest/upgrades/minor-upgrade/

Location(s)

https://docs.timescale.com/mst/latest/maintenance/