✨ Cache architecture for each instance type in memory to avoid unnecessary AWS API requests

[AndiDog]

What type of PR is this?

/kind feature

What this PR does / why we need it:

With the MachinePool Machines feature gate turned on, we now see a lot more reconciliation queueing on large MCs due to reconciling a lot of AWSMachine objects. This PR was a low-hanging fruit: the DescribeInstanceTypes AWS request is 100% cacheable.

This uses CAPI's caching helper and uses a very long caching duration as I don't expect the instance type to architecture mapping to change within AWS.

Confirmed working in our fork already (giantswarm#638).

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
n/a

Special notes for your reviewer:

Checklist:

• squashed commits
• includes documentation
• includes emoji in title
• adds unit tests
• adds or updates e2e tests

Release note:

Cache architecture for each instance type in memory to avoid repeated AWS API requests

[k8s-ci-robot]

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[k8s-ci-robot]

@AndiDog: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-aws-e2e-blocking	7f0b7ad	link	true	/test pull-cluster-api-provider-aws-e2e-blocking
pull-cluster-api-provider-aws-test	7f0b7ad	link	true	/test pull-cluster-api-provider-aws-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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