Add counter support to REST Explorer

[andybons]

Refs: #68363 (ConcurrentTransactionTest#test_transaction_isolation__read_committed, first hit Aug 12)

Setup a table:

CREATE TABLE "developers" ("id" bigserial primary key, "name" character varying, "first_name" character varying, "salary" int DEFAULT '70000', "firm_id" bigint, "mentor_id" int, "legacy_created_at" timestamp, "legacy_updated_at" timestamp, "legacy_created_on" timestamp, "legacy_updated_on" timestamp);
 insert into developers (id) values (1);

In shell 1, type:

BEGIN;
SELECT "developers"."id", "developers"."name", "developers"."salary", "developers"."firm_id", "developers"."mentor_id", "developers"."legacy_created_at", "developers"."legacy_updated_at", "developers"."legacy_created_on", "developers"."legacy_updated_on" FROM "developers" WHERE "developers"."id" = 1 LIMIT 1;
UPDATE "developers" SET "salary" = 200000 WHERE "developers"."id" = 1;

In shell 2, run:

BEGIN;

SELECT "developers"."id", "developers"."name", "developers"."salary", "developers"."firm_id", "developers"."mentor_id", "developers"."legacy_created_at", "developers"."legacy_updated_at", "developers"."legacy_created_on", "developers"."legacy_updated_on" FROM "developers" WHERE "developers"."id" = 1 LIMIT 1;

Back to shell 1:

SELECT "developers"."id", "developers"."name", "developers"."salary", "developers"."firm_id", "developers"."mentor_id", "developers"."legacy_created_at", "developers"."legacy_updated_at", "developers"."legacy_created_on", "developers"."legacy_updated_on" FROM "developers" WHERE "developers"."id" = 1 LIMIT 1;

UPDATE "developers" SET "salary" = 80000 WHERE "developers"."id" = 1;

SELECT "developers"."id", "developers"."name", "developers"."salary", "developers"."firm_id", "developers"."mentor_id", "developers"."legacy_created_at", "developers"."legacy_updated_at", "developers"."legacy_created_on", "developers"."legacy_updated_on" FROM "developers" WHERE "developers"."id" = 1 LIMIT 1;

COMMIT;

Now in shell 2, we see a salary 200000, which is a dirty read (we never committed a salary of 200000):

SELECT "developers"."id", "developers"."name", "developers"."salary", "developers"."firm_id", "developers"."mentor_id", "developers"."legacy_created_at", "developers"."legacy_updated_at", "developers"."legacy_created_on", "developers"."legacy_updated_on" FROM "developers" WHERE "developers"."id" = 1 LIMIT 1;
;
  id | name | salary | firm_id | mentor_id | legacy_created_at | legacy_updated_at | legacy_created_on | legacy_updated_on
-----+------+--------+---------+-----------+-------------------+-------------------+-------------------+--------------------
   1 | NULL | 200000 |    NULL |      NULL | NULL              | NULL              | NULL              | NULL
(1 row)

This can take a bit of time to reproduce (i've had to do this a few times each reproduction), but an external ORM, the contributor to the ORM and I have hit it multiple times, so it is not a fluke.

Jira issue: CRDB-10701