Improve testing of cluster state metadata

[matriv]

In an attempt to improve our bwc, add more DB objects (or more complex objects) which are stored in cluster state, to test seamless rolling upgrade between versions:

DB "objects":

• users/roles (double check if something more could be added)
• privileges
• UDFs (double check if something more could be added)
• views
• publications
• subscriptions
• fdw

Table features:

• default column values/expressions
• Constraints / checks
• Generated column s
• Partitions
  (combination with different types for the above)
  • check table/partition version after upgrade steps(?)

[jeeminso]

Trying to add a crate-qa test for crate/crate#17574 and crate/crate#17575. But it requires 2 upgrades to be able to replicate the scenarios, 5.4 > 5.7 > 5.9 where the current bwc tests are limited to only 1 upgrade. I think we can consider testing series of upgrades and also testing (dynamic)column names of the results set and assigned oids(somehow).
update: I had a wrong idea about the bwc tests.