sql: add support for INSTEAD OF triggers

[DrewKimball]

This issue tracks adding support for INSTEAD OF triggers to CRDB. INSTEAD OF triggers only operate on views, and completely replace the original mutation operation. They can only be row-level triggers. Generally, an INSTEAD OF trigger maps from a mutation on the view to mutations on the underlying base tables. It is not possible to define a trigger on a materialized view.

Note that CRDB does not currently support direct mutations on views like Postgres does, tracked in https://github.com/cockroachdb/cockroach/issues/20948. This shouldn't be an obstacle to implementing INSTEAD OF triggers, since they entirely replace the mutation anyway.

Epic CRDB-347

Jira issue: CRDB-39863

Jira issue: CRDB-39863

Jira issue: CRDB-39863