Adding AL2 UserData Merge Support

[suket22]

• Adding AL2 Merge Support

1. Issue, if available:
#885

2. Description of changes:

• Adds UserData support for AL2. This is the first step for the support, where we merge UserData contents in the MIME multi part sequence of Customer Managed -> Karpenter Managed.
  • In a subsequent PR, I'll enable the ability to override kubeletConfiguration and container-runtimeConfiguration as well.

3. How was this change tested?
I tested this locally by creating the necessary resources and scaling the inflate pods. Also verified that the docs links were correct.

> cat provisionerAl2.yaml
apiVersion: karpenter.sh/v1alpha5
kind: Provisioner
metadata:
  name: default
spec:
  limits:
    resources:
      cpu: 20
  provider:
    amiFamily: AL2
    instanceProfile: KarpenterNodeInstanceProfile-karp-cluster
    subnetSelector:
      karpenter.sh/discovery: karp-cluster
    securityGroupSelector:
      karpenter.sh/discovery: karp-cluster
  providerRef:
    name: al2
  ttlSecondsAfterEmpty: 30
---
apiVersion: karpenter.k8s.aws/v1alpha1
kind: AWSNodeTemplate
metadata:
  name: al2
spec:
  userData: |
    MIME-Version: 1.0
    Content-Type: multipart/mixed; boundary="BOUNDARY"

    --BOUNDARY
    Content-Type: text/x-shellscript; charset="us-ascii"

    #!/bin/bash
    echo "Running custom user data script"

    --BOUNDARY--

4. Does this change impact docs?

• Yes, PR includes docs updates
• Yes, issue opened: link to issue
• No

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

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[ellistarn]

Can we frame this page as a single "launch templates" story that talks about everything? To start, we can just include the content you have and elaborate from there.

Suggested change

	Review the [Custom UserData documentation](../user-data/) to learn the necessary steps.
	Review [Custom Launch Templates](../launch-templates/) to learn the necessary steps.

[suket22]

I called it Custom UserData to distinguish it from this doc https://karpenter.sh/v0.10.1/aws/launch-templates/ that's titled Launch Templates and Custom Images.

Not sure what terminology would fit better.

[ellistarn]

Let's collapse it later.

[ellistarn]

From our discussion, I thought provider and providerRef was an OR semantic. The user would need to specify these in in the AWSNodeTemplate.

[suket22]

That's a much larger change to make. I can work on it in a separate PR - do you think we should disable this feature until that's complete?

[ellistarn]

Yeah probably. Only because it will break early adopters.

[ellistarn]

LGTM. A few minor comments.