Add per-query memory pool configuration

### Problem

https://github.com/influxdata/influxdb/pull/26429 introduced a new feature available to the query `Executor` configuration that is used for the underlying `iox_query` engine: `per_query_mem_pool_config`.

This uses the [`PerQueryMemoryPoolConfig` type](https://github.com/influxdata/influxdb3_core/blob/fd0e474a6c0af5ba867399d753f5df18f59907cb/iox_query/src/memory_pool.rs#L81-L119).

We are currently not leveraging this feature.

### Proposed solution

Add a `--per-query-memory-pool-size` CLI argument to the `serve` command that allows a user to optionally set the size of the per query memory pool.

Start by reading PR #26429 and the PerQueryMemoryPoolConfig definition in iox_query/src/memory_pool.rs, then trace how the serve command builds its query Executor configuration. Add the optional --per-query-memory-pool-size setting and verify that its value reaches the per-query memory pool configuration.

Written by the indexing model from the issue text.