Is there any easy way to search the release notes to see when a certain functionality was added?

You can search the CHANGELOG.md file

I’m trying to find ASG Warm Pools were added to the AWS Package specifically and can’t find it by doing any search in the changelog

The AWS package is built on the AWS Terraform provider so you'll see frequent messages in pulumi's AWS package changelog like:

Upgrade to v3.40.0 of the AWS Terraform Provider

Maybe you should look at the terraform aws provider changelog and match it?

I think you’re right, if that’s all the callout is

yup, @bored-oyster-3147 is correct, that will be the case for the majority of tf provider updates