Reduce the amount of authentication requests

[devigned]

/kind feature

Describe the solution you'd like
For every reconciliation, CAPZ will completely rebuild the cluster Authorizer and with it, cause a request to Azure Active Directory to procure a new JWT which will them be used to Authenticate to Azure. You can see the POST in the Jaeger output below.

Azure Active Directory generally responds in about 80ms - 200ms, but this is overhead for every reconcile cycle. It adds up. Also, it's not very friendly to Azure Active Directory.

I think we can use the work in #1067, specifically, the Authorizer.Hash() and the time to live least recently used cache to create a safe and efficient mechanism to reuse Authorizers across reconcile cycles.

[CecileRobertMichon]

/priority important-longterm

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/lifecycle stale

[CecileRobertMichon]

/remove-lifecycle stale

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/lifecycle stale

[CecileRobertMichon]

/remove-lifecycle stale

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/lifecycle stale

[devigned]

/remove-lifecycle stale