sql: add randomized tests for plan pinning

[michae2]

After finishing #170360, #170680, and #170692, we should add two randomized tests for plan pinning:

1. A test that (a) generates a random query, (b) uses EXPLAIN (OPT, PLANGRAM) to get the PlanGram, (c) pins the plan using the PlanGram, and then (d) validates that a PlanGram match was found and EXPLAIN (OPT, PLANGRAM) is the same.
2. A test that (a) generates a random query, (b) uses EXPLAIN (GIST) to get the plan gist, (c) pins the plan using the plan gist, and then (d) validates that a PlanGram match was found and EXPLAIN (GIST) is the same.

Jira issue: CRDB-64122