Improve the error handling for database schema upgrades

[michaelnoonan]

When supporting some customers, including those hosted by Octopus Cloud, it became evident some additional comfort could be offered when we have problems upgrading the database schema. This can be quite discomforting for customers, and we should be very clear about:

1. The state of their database
2. What they can do to get back up and running
3. How to get help if they need it

[octoreleasebot]

Release Note: Improved messaging for different failure scenarios when running the database schema upgrades to be clearer about the state of their database, what they can do to get back up and running, and how to get help if they need it

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