PGX SimpleProtocol test suite (#10198)

## What changed?
Adds TestPGXSimpleProtocol — a new entry in the persistence integration
suite that runs `PostgreSQLSuite` under the `postgres12_pgx` plugin with
`default_query_exec_mode=simple_protocol`.

## Why?
Regression coverage for issues like
[#9804](https://github.com/temporalio/temporal/issues/9804). With pgx ≤
v5.9.1, current_executions.state/status (proto-enum-typed int32 fields
with a String() method) were text-encoded via fmt.Stringer and rejected
by `Postgres` on simple/exec protocol, the path users land on behind
PgBouncer in transaction pooling. pgx v5.9.2 fixed it upstream; this
test makes sure we notice if pgx is ever downgraded or if a similar
issue sneaks in.

## How did you test it?
- [X] built
- [X] run locally and tested manually
- [ ] covered by existing tests
- [ ] added new unit test(s)
- [X] added new functional test(s)

Verified locally: passes on pgx v5.9.2; fails reproducibly on v5.9.1
with invalid input syntax for type integer: "Created" matching
[#9804](https://github.com/temporalio/temporal/issues/9804).

## Potential risks
Adds one additional pass through PostgreSQLSuite to the Integration test
job. Job timeout is 15 min, so should be fine, but worth observing.