Add guidance for setting the timeout value for PG upgrades

Overview

When upgrading PostgreSQL using the pg-upgrade command, if the upgrade fails due to a timeout, there is no guidance on how to proceed, leaving the user wondering how they will be able to upgrade their data to the new PostgreSQL version without further timeout issues.

Proposal

• Currently, the error that is output is simply "timed out". Change the error message to read "A timeout occurred. The default timeout is xx. To change the timeout value, run gitlab-ctl pg-upgrade -V <version> -T <timeout_value_in_milliseconds>.
• Add a troubleshooting section to https://docs.gitlab.com/omnibus/settings/database.html#upgrade-packaged-postgresql-server that explains what to do if a postgresql upgrade fails. In this section, include tips on dealing with a timeout issue. We should also include instructions for removing the new directory discussed in #5317 (closed).

#5316 (closed) adds the option to use other units. We should complete that issue first and add a note to the error message about options for specifying the unit.