Only add singleton list API converters for the existing APIs

[ulucinar]

Description of your changes

Only apply the CRD API conversions for converting between singleton list & embedded object APIs for the already existing resources with the generated singleton list CRD APIs.

When we try to add a new Terraform resource with a singleton list in its schema, currently, we need to do a manual configuration such as the following:

p.AddResourceConfigurator("azurerm_pim_active_role_assignment", func(r *config.Resource) {
		r.PreviousVersions = nil
		r.Version = "v1beta1"
		r.Conversions = nil
		r.TerraformConversions = []config.TerraformConversion{
			config.NewTFSingletonConversion(),
		}
	})

, so that the API converters registered are removed and versioning starts with v1beta1 instead of v1beta2 (for such new resources, the v1beta1 version does not already exist).

This PR records the names of resources with previous CRD APIs containing (now converted) singleton lists so that the API converters are only registered for them.
This makes adding new resources with singleton lists in their Terraform schemas easier by removing the need to do a manual configuration like shown above.

The newly introduced list should mostly be immutable (it records a set of existing resources with a specific condition at a point in time). Bugs may result in exceptions where we may need to update this list. In other words, new resources should normally be never added to this list, doing so will result in an invalid configuration.

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Via the following uptest runs:

• NodeGroup.v1beta2.eks (the v1beta2 manifest contains a converted embedded object relevant in our context): https://github.com/crossplane-contrib/provider-upjet-aws/actions/runs/9518567085
• DeliveryStream.v1beta2.firehose: https://github.com/crossplane-contrib/provider-upjet-aws/actions/runs/9518491580
• SecurityConfig.v1beta1.opensearchserverless (contains an embedded field (samlOptions) represented as a single nested block in the Terraform schema): https://github.com/crossplane-contrib/provider-upjet-aws/actions/runs/9518549846

[ulucinar]

/test-examples="examples/firehose/v1beta2/deliverystream.yaml"

[ulucinar]

/test-examples="examples/opensearchserverless/v1beta1/securityconfig.yaml"

[ulucinar]

/test-examples="examples/eks/v1beta2/nodegroup.yaml"

[mergenci]

Thanks @ulucinar 🙏 This PR should make new resource configurators' job significantly easier by eliminating the need to understand the shenanigans of singleton list conversions. Please see my suggestion regarding documentation below.

[ulucinar]

/test-examples="examples/firehose/v1beta2/deliverystream.yaml"