chore: enable local CI to run in parallel and leave quick-start clusters alone

[richcooper95]

In #318 we introduced the ability to run our CI locally via act. This is extremely helpful, but currently very slow to run the unit/system/integration tests all together, since they need to be run serially. The integration tests also still use the same cluster names as the defaults in the quick-start, meaning any cluster spun up manually will be destroyed when running the integration tests locally.

To enable proper parallelisation, there are a couple of things left to do, detailed below...

Parametrise ports to enable parallelisation

The work for #318 included parametrising the platform/worker cluster names in the system tests (e.g. from kind-platform -> kind-system-test-platform) so that each suite would have its own cluster spun up independently. However, we discovered that the ports we expose also clash between suites and manually-provisioned quick-start clusters (e.g. 31340 for Backstage, 31333 for Gitea).

These ports will need to be unique per test suite, and passed in as parameters to the system/integration tests (with the current values used as defaults).

Use unique cluster names for integration tests

The system tests already use the system-test- prefix for cluster names, but the integration tests don't. We'll need to introduce a similar integration-test- prefix to the cluster names to prevent clashing with the quick-start defaults.