[fix] make VLAN IPs unique across controller pod restarts

[tchinmai7]

What this PR does / why we need it:
With the VLAN clusters, a in-memory map was maintained for each cluster's IPs. When the controller pod restarts, that IP map is lost, and any further cluster scaling activities cause the nodes to get overlapping IPs.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:
Testing steps

1. run make local-deploy off main
2. Create a cluster with the rke2-vlan flavor
3. Delete the capl-controller pod
4. Increase the number of replicas in the md. describe the linodemachines and see that more than one linode has the same vlanIP
5. run make local-deploy off this branch
6. Delete one of the problem linodemachines
7. Repeat the steps and verify that all machines now have a unique IP

TODOs:

• squashed commits
• includes documentation
• adds unit tests
• adds or updates e2e tests

[codecov]

Codecov Report

Attention: Patch coverage is 39.21569% with 31 lines in your changes missing coverage. Please review.

Project coverage is 63.63%. Comparing base (2c91eb4) to head (1d81702).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
util/vlanips.go	50.00%	14 Missing and 6 partials ⚠️
controller/linodemachine_controller_helpers.go	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #544      +/-   ##
==========================================
- Coverage   64.82%   63.63%   -1.20%     
==========================================
  Files          79       79              
  Lines        4299     5486    +1187     
==========================================
+ Hits         2787     3491     +704     
- Misses       1242     1719     +477     
- Partials      270      276       +6     

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[AshleyDumaine]

nit:

Suggested change

	if addr.Type == clusterv1.MachineInternalIP {
	if ipnet.Contains(net.ParseIP(addr.Address)) {
	existingIPs = append(existingIPs, addr.Address)
	}
	}
	if addr.Type == clusterv1.MachineInternalIP && ipnet.Contains(net.ParseIP(addr.Address)) {
	existingIPs = append(existingIPs, addr.Address)
	}

[AshleyDumaine]

small nit, otherwise LGTM