Use EKS node pool configuration by default

### Description / Background

We previously had a problem with node pool configuration in EKS bulk import, that caused us to disable it by default:
- https://github.com/gchq/sleeper/issues/7851
- https://github.com/gchq/sleeper/issues/7863

We think we've resolved this as of the second issue, so we can enable it by default, and ensure it's included in the system tests.

### Technical Notes / Implementation Details

This is the instance property `sleeper.bulk.import.eks.automode.nodepool.enabled`.

We can also change the default for `sleeper.bulk.import.eks.cluster.type` to `automode`.

#### System tests

We can read through EksAutoBulkImportST or EksBulkImportPerformanceST and their instance configuration, to make sure there's nothing that will override this, and ensure they will use the default node pool configuration.

Start by reading EksAutoBulkImportST and EksBulkImportPerformanceST, along with their instance configuration, to find any overrides of sleeper.bulk.import.eks.automode.nodepool.enabled or sleeper.bulk.import.eks.cluster.type. Verify the defaults enable the node pool configuration and select automode, then run the relevant system tests to confirm they use those defaults.

Written by the indexing model from the issue text.