[kots]: add node CPU/memory check tests to workspace node only

[mrsimonemms]

Description

Applies tests on the CPU/memory to the workspace nodes only. Our requirements only stipulate the performance of these nodes, not all the nodes in the cluster.

This also changes the wording for the CPU tests to change "cluster" to "node" (a remnant of when we had the tests on a cluster basis).

Related Issue(s)

Fixes #9307

How to test

Run the preflight checks

Release Notes

[kots]: add node CPU/memory check tests to workspace node only

Documentation

Werft options:

• /werft with-preview

[lucasvaltl]

👋 Do we have a minimum requirement for the non-workspace nodes though? I fear that there might be a case where someone uses an underpowered node for the server component for example and then wonders why. We did have another related issue (#10867) asking for a per-node label hardware requirement. How difficult would that be to implement?

[mrsimonemms]

Honestly, I don't know what the requirements for the non-workspace nodes are. To the best of my knowledge, these aren't documented anywhere so one assumes that there aren't any explicit requirements.

I think these two tickets are pretty much a duplication of each other, albeit with a slightly different focus (#10867 is about the general required whereas #9307 is about how this is tested in KOTS).

The implementation for #10867 is very easy once we have the requirements. My feeling is that that ticket has three phases:

1. Get the requirements from the specific teams
2. Add this into the documentation
3. Add this into KOTS (this will end up looking very similar to this PR, except with other node labels)

[nandajavarma]

Changes look good! Didn't test it.

[lucasvaltl]

Did we want to merge this already?

[mrsimonemms]

@lucasvaltl I think it's fine that this is merged in as it was technically incorrect (see #9307). We can raise the additional things as a future PR to make it even more correct