fix: Set output.image_id to be the real output of the launch template

[bushong1]

Description

Fixes issue #2235 ; configure the output of image id to be the real output of the launch_template

Motivation and Context

#2235

Breaking Changes

If a user provided a custom ami_id and relied on the broken information this submodule was returning, they could see a change in behavior as the output corrects itself.

How Has This Been Tested?

• [ ] I have updated at least one of the examples/* to demonstrate and validate my change(s)
• [x] I have tested and validated these changes using one or more of the provided examples/* projects
  • examples/self_managed_node_group
  • Run: terraform output -json | jq .self_managed_node_groups.value.bottlerocket.image_id
    • Value before change: ami-0f2b7c6874eb8414f (The default AMI, despite being overridden in the config)
    • Value after change: ami-04958b57e72e69fb0 (The actual bottlerocket ami id)

• [x] I have executed pre-commit run -a on my pull request