[CPDEV-101682] Support single control plane cluster

[ilia1243]

Description

• If no nodes with control-plane role are provided, Kubemarine fails with internal error.
• At least one control-plane node is necessary even for connection-only enrichment
  • choose default node in do procedure
  • preserve information about the procedure run.
• In contrast, it is potentially possible to install the cluster with the only control-plane node for dev aims.
  • In particular, this allows to rebuild the only worker node using remove & add node while temporarily persisting only control planes.

Solution

• Raise exception if no control planes are specified in the inventory.
• Allow clusters without workers.

Test Cases

TestCase 1

Rebuild the only worker node using remove & add node.

Steps:

1. Install the cluster with 1 worker and 1 control-plane.
2. Remove the only worker.

Results:

Before	After
KME0004	Node is removed successfully

3. Add the worker.

ER: Node is added successfully.

TestCase 2

Install single control plane cluster.

Steps:

1. Configure inventory

   nodes:
   - name: control-plane
     internal_address: <address>
     roles: [control-plane]
   services:
     coredns:
       deployment:
         spec:
           template:
             spec:
               nodeSelector:
                 node-role.kubernetes.io/worker: null
   plugins:
     nginx-ingress-controller:
       install: false

2. Install the cluster.

Results:

Before	After
KME0004	Cluster is installed successfully

3. Upgrade the cluster.

ER: Cluster is upgraded successfully.

TestCase 3

Try to install cluster without control planes.

Steps:

1. Try to install cluster without control planes.

Results:

Before	After
Internal error	KME0004

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Integration CI passed
• Unit tests. If Yes list of new/changed tests with brief description
• There is no merge conflicts

Unit tests

test_defaults.yaml - cover new functionality and validation.