Connection reset adding tables via REST API

### Description / Background

On 26/08/2026 the nightly system tests reported two test failues.
Quick - PartitionSplittingST.shouldSplitPartitionsWith100RowsAndThresholdOf20
Slow3 - MultipleTablesST.shouldGenerateMetricsForMultipleTables

Both showed:
[java.io](http://java.io/).UncheckedIOException: [java.io](http://java.io/).IOException: Connection reset
at sleeper.systemtest.drivers.instance.AwsSleeperTablesDriver.addTableViaRest(AwsSleeperTablesDriver.java:123)

This has recurred every day since then, and we raised a separate issue to disable the REST API in system tests:
- https://github.com/gchq/sleeper/issues/8024

When we fix this, we can re-enable use of the REST API in the system tests.

### Steps to reproduce

1. Check system test logs
2. See error

### Expected behaviour

These tests should pass consistently. I assume these aren't the only tests adding tables via the Rest API so investigation will need to be taken on what went wrong, followed by how we can strengthen the tests to prevent this.

Start with sleeper.systemtest.drivers.instance.AwsSleeperTablesDriver.addTableViaRest at line 123 and the system test logs for PartitionSplittingST.shouldSplitPartitionsWith100RowsAndThresholdOf20 and MultipleTablesST.shouldGenerateMetricsForMultipleTables. Investigate why adding tables through the REST API resets the connection and whether other system tests use the same path. Done means the affected tests pass consistently and REST API use can be re-enabled in system tests.

Written by the indexing model from the issue text.