Add Cluster UID in Loadbalancer name and Droplet target tag

[prksu]

What this PR does / why we need it:
This PR adds Cluster UID in Loadbalancer name and adds an additional tag that contains Cluster UID for droplet target tag to allow creating two or more clusters with the same name but different namespace in the single management cluster.

Which issue(s) this PR fixes:
Fixes #217

Special notes for your reviewer:
/cc @timoreimann

Release note:

Add Cluster UID in Loadbalancer name and Droplet target tag

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[timoreimann]

This looks good to me in general.

@prksu should we try to accompany the change with an e2e test to guarantee it's working for sure?
I realize this would effectively implement #185. If that sounds like too much work, we could also punt on that for now (but should probably have one before the next release IMO), and maybe do a quick manual test instead. WDYT?

[prksu]

@timoreimann so far I just do a manual test and it works as expected.

$ kubectl get cluster -A
NAMESPACE   NAME               PHASE
default     capdo-quickstart   Provisioned
dev         capdo-quickstart   Provisioned
$ doctl compute load-balancer list --format ID,Name,Status,Tag
ID                                      Name                                                               Status    Tag
aca64495-63b9-48c6-9ea9-59d9df65c45d    capdo-quickstart-apiserver-f7777de0-315c-466d-a9de-07121680b75f    active    sigs-k8s-io:capdo:capdo-quickstart:f7777de0-315c-466d-a9de-07121680b75f:apiserver
5309ee41-34ea-4e3d-9802-a955af256156    capdo-quickstart-apiserver-b72a8475-c71e-4fe4-b73a-b98c81afcf0c    active    sigs-k8s-io:capdo:capdo-quickstart:b72a8475-c71e-4fe4-b73a-b98c81afcf0c:apiserver

And yes, it would be good to add e2e for this, let's make e2e as a follow-up. the test would be creating two capdo clusters with the same cluster-name in the different namespace.
actually, #185 is for LB creation from Service (created by CCM), the LB creation for control-plane itself already covered in current e2e.

[timoreimann]

@prksu makes total sense to me. Thanks a bunch for driving this one. 👍

/lgtm