[aws-for-fluent-bit] Replaced docker.io image repo by public ECR

[mickeypash]

It would make sense that all EKS charts now use the ECR Public
repository. [re #356]

Issue

Description of changes

• Update remaining DockerHub-hosted repositories to use ECR #356
• You can find the image here

Checklist

• Added/modified documentation as required (such as the README.md for modified charts)
• Incremented the chart version in Chart.yaml for the modified chart(s)
• Manually tested. Describe what testing was done in the testing section below
• Make sure the title of the PR is a good description that can go into the release notes

Testing

• Tested on an internal k8s cluster.

helm upgrade --install aws-for-fluent-bit eks/aws-for-fluent-bit 
    -n kube-system \
    -f helm/fluent-bit.yml \
    --debug \

Way of checking which image is being used

kubectl get pods -l app.kubernetes.io/name=aws-for-fluent-bit \
-n kube-system -o jsonpath="{.items[].spec.containers[].image}" \
 | tr -s '[[:space:]]' '\n' \
 | sort \
 | uniq -c

1 public.ecr.aws/aws-observability/aws-for-fluent-bit:2.21.5

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

[jaypipes]

👍 thank you @mickeypash!