migrations: persist the version setting for 1.1-initialized clusters

[tbg]

As a follow-up to #17216, we want to make sure that there is always a persisted version cluster setting for folks running 1.1. In particular, this means that a new cluster initialized using v1.1 should have a persisted version setting.

@dt pointed out in #17216 that there is a precedent:

#17216 (comment)

For the diagnostic reporting setting, semantically we wanted a default of true, but since settings need to be allowed to return defaults until they are read and didn't want to risk ignoring an explicit false and betraying user trust, we went with a default of false with a startup migration writing an explicit true (optInToDiagnosticsStatReporting in migrations.go). This feels pretty similar.