📖 Update optional fields in docs for Machine and Cluster controllers

[Jont828]

What this PR does / why we need it: Update optional fields in docs for Machine and Cluster controllers
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 #7300 #7301

[oscr]

/lgtm

Content looks accurate based on the code.

Not related to this pr but a general question. How detailed should the documentation be? When it becomes this detailed it's getting very close to just reading the code or the godoc. Comparing:

FailureDomainSpec` is defined as:
- `controlPlane` (bool): indicates if failure domain is appropriate for running control plane instances.
- `attributes` (`map[string]string`): arbitrary attributes for users to apply to a failure domain.

with https://pkg.go.dev/sigs.k8s.io/[email protected]/api/v1alpha4#FailureDomainSpec

[killianmuldoon]

/lgtm

IMO having these definitions be close to the godoc isn't necessarily a bad thing as the godoc isn't a great source of information for the contract definition.

I think these pages are close to the source of truth for the reality of the provider contracts, so having field information that's close to the level of detail of the godoc isn't IMO an issue.

[fabriziopandini]

/lgtm
@sbueringer PTAL

[sbueringer]

Sorry, last nits from my side. Just noticed that the current definition of addresses are not entirely correct

[oscr]

@Jont828 Could you please also squash your commits? If you don't know how it's described in CONTRIBUTING

[Jont828]

@oscr Done, let me know if there's anything else I need to do to get this merged!

[sbueringer]

Thank you very much!

/lgtm
/approve

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