make schema_versions::KNOWN_VERSIONS const

[iliana]

Every time I add a database migration I stare at this and think "that could be const". I think I've finally figured out a non-obtrusive way to do it.

There's a handful of other unnecessary uses of LazyLock in Omicron that I want to go clean up but this one probably is worth having its own review.

[iliana]

(If you didn't know, you can more easily review PRs like this with heavy whitespace changes by adding ?w=1: https://github.com/oxidecomputer/omicron/pull/7677/files?w=1)

[iliana]

Looking it up, I think this probably ought to be a static even if we can remove the LazyLock so it is only present in the binary once. Actually wait, because it’s a slice the “const” should be the memory reference and therefore small…