[GEP-28] Add InternalIPs to CreateMachineResponse

[jamand]

How to categorize this PR?
/kind enhancement
/platform openstack

What this PR does / why we need it:

Server InternalIPs are now returned on created Machines, so that they may be used by gardenadm bootstrap (GEP-28). This is useful when the already provided hostname field (in the Machine status.addresses) is not resolvable, e.g. due to cloud provider specific settings.

Which issue(s) this PR fixes:
Fixes #321

Special notes for your reviewer:
/cc @timebertt @maboehm

• Currently relies on gardener/machine-controller-manager@52f840e to avoid container crashes, requires a new release.
• Added a new test case (to check having a pool with multiple internal IPs) + extended happy path.
• Tested on own environment (with Garden, multiple Seeds, Shoots on the gardener/gardener v1.128.4 version), using the Medium touch scenario: in a virtual cluster the Machine resource is created and the InternalIP is set in the Machine Status.

Release note:

When calling CreateMachine() the method now returns the internal IPs of the server in the Addresses field. 

[CLAassistant]

All committers have signed the CLA.

[gardener-robot-ci-3]

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[timebertt]

cc @kon-angelo @hebelsan can you help us get a review here?

[kon-angelo]

/assign

[kon-angelo]

I had already looked at the change but forgot to post the review 😅 .

I assume there is no other way to get a more "structured" response from the addresses field. I also had a look at the client but I didn't think anything better.

[kon-angelo]

/needs rebase

[jamand]

@kon-angelo Thanks for the Review! In order to remove the current dependency on this particular commit (already on main) I would need a new (patch) release of https://github.com/gardener/machine-controller-manager. I would then do a rebase.
Can you do that or who should I ask?

Also to your point with the "structured" response from the addresses field: I'm also not super happy about it, here the OpenStack API Reference is equally vague with type "object" and the description consult with OpenStack Networking API for up-to-date information.