Update CFN Template of AWS unified Firehose to integrate with Metrics Forwarder lambda

[hrai-nr]

This code changes update CFN Template of AWS unified Firehose to integrate with Metrics Forwarder lambda.
Here is the approach:

1. Store firehose instrumentation version in the template using Mappings.
2. At the time of release of template to S3 bucket, get latest value of instrumentation version from version.yaml and change the mapping defined in step 1.
3. At the time of calling metrics forwarder template, use this mapping to create the required JSON.

Testing :

1. Testing that the JSON passed to second stack is correct,

2. To test the release workflow, that the mapping is getting replaced dynamically, used cat statements to print the entire content of templates, and checked before and after by created a dummy workflow. The workflow was triggered by raising the PR and changes were tested.

[maya-jha]

How was this tested?

[hrai-nr]

How was this tested?

I have added the testing method and result in PR description