EKS self managed node group support

[richardcase]

/kind feature

Describe the solution you'd like
When creating an EKS cluster i want to provision a "self managed node group" that uses an EC2 instance for worker nodes. Will need to use the boostrap data from #1779.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-aws version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[rudoi]

Could this and #1785 be solved by implementing MachinePool providers (maybe even #1786 if we're willing to flex the definition of "machine pool")?

"AWSMachinePool", for example, could map to an AutoScalingGroup
"AWSManagedMachinePool" (or even just "AWSManagedNodeGroup", names are hard) could map to a Managed Node Group.

I've worked very little with Fargate profiles so I'm not quite sure how that would go at present.

[rudoi]

/assign @mytunguyen
/assign @nicoleyson

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In response to this:

/assign @mytunguyen
/assign @nicoleyson

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[nicoleyson]

/assign @mytunguyen