The incorrect AMI ID is being passed from the UI to the config file

[saji-pivotal]

Bug description
IaaS: AWS
The AMI ID of the OS image being specified in the UI is not being correctly passed to the config file.
This is not critical as the AMI ID is deprecated, but this still makes for a poor user experience.

Affected product area (please put an X in all that apply)

• APIs
• Addons
• CLI
• Docs
• Installation
• Plugin
• Security
• Test and Release
• User Experience

Expected behavior
The AMI ID of the OS Image being used should be used to populate the AWS_AMI_ID field in the cluster configs

Steps to reproduce the bug

1. Run tanzu management-cluster create --ui
2. Go through the steps of creating a management cluster on AWS
3. Select Ubuntu from the dropdown of available OS Images
4. Once the cluster config file is populated, DO NOT continue creating a management cluster
5. Open the cluster config file and inspect the AWS_AMI_ID field. It will most likely be incorrect. It will correspond to the AMI ID of the OS that is listed first in the BOM being used.

Version (include the SHA if the version is not obvious)
1.3.0

Environment where the bug was observed (cloud, OS, etc)
AWS

Relevant Debug Output (Logs, manifests, etc)

[saji-pivotal]

The PR for fixing this issue is #558