roachtest: add schemachange/database-version-upgrade

[thoszhang]

This PR adds a new mixed-version roachtest, which tests 2 loosely
related things:

1. Correctness of database schema changes during the 20.1/20.2 mixed-
   version state, in which 20.2 nodes still use the deprecated database
   cache and non-lease-based schema change implementation.
2. Ability to use ALTER DATABASE ... CONVERT TO SCHEMA WITH PARENT on
   databases created in 20.1.

To these ends, the test creates several databases, runs schema changes
on each one at different states in the rolling upgrade process, and runs
the reparenting statement on all of them post-finalization.

Closes #53568.

Release note: None

[cockroach-teamcity]

This change is 

[thoszhang]

I was originally trying to jam this into acceptance/mixed-version but decided against it, both because this needs a true mixed-binary-version state and because I was originally worried about interactions with the introspection in the schema change workload (though I then realized this isn't hard to avoid since the workload uses prefixes for its own names). So now this is a separate roachtest. Maybe the reparented databases could stand to have more stuff in them.

[ajwerner]

Maybe the reparented databases could stand to have more stuff in them.

I agree but am not going to block this good stuff over that.

Reviewed 1 of 2 files at r1.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @ajwerner)

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pkg/cmd/roachtest/schema_change_database_version_upgrade.go, line 1 at r1 (raw file):

package main

lint stuffs

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pkg/cmd/roachtest/schema_change_database_version_upgrade.go, line 204 at r1 (raw file):

		createParentDatabaseStep,
		reparentDatabaseStep("db_0"),
		reparentDatabaseStep("db_1"),

If I had one nit it'd be that it might be nice to interact with the tables after they've been reparented. It's just a suggestion though. I'd take this as-is or with a TODO.

[thoszhang]

Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale)

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pkg/cmd/roachtest/schema_change_database_version_upgrade.go, line 1 at r1 (raw file):

Previously, ajwerner wrote…

lint stuffs

Done.

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pkg/cmd/roachtest/schema_change_database_version_upgrade.go, line 204 at r1 (raw file):

Previously, ajwerner wrote…

If I had one nit it'd be that it might be nice to interact with the tables after they've been reparented. It's just a suggestion though. I'd take this as-is or with a TODO.

I added some schema changes at the end.

[thoszhang]

TFTR

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)