Cluster-api-provider-azure: expose cloud provider rate limiting configuration

[alexeldeib]

/kind feature

Describe the solution you'd like
The Azure cloud provider exposes a wide number of configuration fields: https://github.com/kubernetes-sigs/cloud-provider-azure/blob/master/docs/cloud-provider-config.md#cloud-provider-config

Most of these can be derived from infrastructure specs in CAPZ. The significant outliers all are around the rate limiting configuration for the cloud provider. We should surface these to users in a reasonable way without requiring them to set the entire file.

One approach would be to allow the subset of the CloudProviderConfig struct relevant to rate limiting to be defined in a config map. We would merge any user provided values there over our own defaults when we build the configuration.

Anything else you would like to add:
Follow up to #802

[alexeldeib]

@marwanad any thoughts on this? would it be reasonable to just expose a config map for the rate limiting config?

[marwanad]

I'd say a configmap and merge with defaults is probably reasonable - yeah

[alexeldeib]

For comparison sake, we could also embed it directly into the spec

[nader-ziada]

would we want to expose all these values? https://kubernetes-sigs.github.io/cloud-provider-azure/install/configs/#per-client-rate-limiting

[CecileRobertMichon]

We could make this a 1.18+ feature only and support per-client rate limiting to avoid having to implement the old way of having global rate limit settings.

[CecileRobertMichon]

/milestone next
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[dr0pdb]

/assign

[dr0pdb]

busy for few weeks.

/unassign

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[CecileRobertMichon]

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