Add support for custom Bottlerocket AMIs for MNG

[koooosh]

Issue

Close: #8419

Description

Currently, when creating MNGs using a custom Bottlerocket AMI with eksctl, we get the error:

Error: could not create cluster provider from options: cannot set amiFamily to Bottlerocket when using a custom AMI for managed nodes, only AmazonLinux2023, AmazonLinux2, UbuntuPro2404, Ubuntu2404, UbuntuPro2204, Ubuntu2204, Ubuntu2004, Ubuntu1804 are supported

This PR adds support for custom Bottlerocket AMIs for MNG.

Also, it improves tests in managed_bottlerocket_test.go so they verify specific settings rather than entire strings 😁

Testing

• make test
• Manual test:

1. Locally built eksctl
2. Manifest with an MNG using a custom Bottlerocket AMI:

apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: br-custom-ami-cluster
  region: us-west-2
  version: '1.31'

managedNodeGroups:
  - name: br-custom-ami-mng
    instanceType: m5.large
    desiredCapacity: 1
    ami: ami-02516a800443b52d6   # aws ssm get-parameters --names "/aws/service/bottlerocket/aws-k8s-1.31/x86_64/1.40.0/image_id" --region us-west-2
    amiFamily: Bottlerocket
    disableIMDSv1: true
    iam:
       attachPolicyARNs:
          - arn:aws:iam::aws:policy/AmazonEKSWorkerNodePolicy
          - arn:aws:iam::aws:policy/AmazonEKS_CNI_Policy
          - arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly
          - arn:aws:iam::aws:policy/AmazonSSMManagedInstanceCore
    bottlerocket:
      settings:
        motd: "Hello from eksctl!"

3. ./eksctl create cluster -f <MANIFEST> successfully creates cluster and MNG with custom AMI

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[koooosh]

bottlerocketSettingsTOML, similar to ProtectTOMLKeys a few lines above, comes from bottlerocket.go and is used to set the kubernetes cluster settings, which is necessary for the nodes to join the cluster.

Without this function, I was seeing the following error in the kubelet logs:

err="failed to construct kubelet dependencies: unable to loadclient CA file /etc/kubernetes/pki/ca.crt: error creating pool from /etc/kubernetes/pki/ca.crt: data does not contain any valid RSA or ECDSA certificates"

[koooosh]

This test passing verifies that these settings cannot be manually set thru userdata, only injected.

[koooosh]

These settings actually exist, but should not be set thru userdata: https://bottlerocket.dev/en/os/1.39.x/api/settings/kubernetes/#node-labels

[cartermckinnon]

lgtm!

[naclonts]

Thanks for the contribution! 🚀