Update builder list in README and update default platform API version

Update outdated builders in README

Some builders listed in the README are outdated and should be updated to reflect current recommendations.

Suggested builders from pack builder suggest are:

Google:

• gcr.io/buildpacks/builder:google-22 - Ubuntu 22.04 base image with buildpacks for .NET, Dart, Go, Java, Node.js, PHP, Python, and Ruby

Heroku:

• heroku/builder:24 - Ubuntu 24.04 AMD64+ARM64 base image with buildpacks for .NET, Go, Java, Node.js, PHP, Python, Ruby & Scala

Paketo Buildpacks:

• paketobuildpacks/builder-jammy-base - Ubuntu 22.04 Jammy Jellyfish base image with buildpacks for Java, Go, .NET Core, Node.js, Python, Apache HTTPD, NGINX and Procfile
• paketobuildpacks/builder-jammy-buildpackless-static - Static base image (Ubuntu Jammy Jellyfish build image, distroless-like run image) with no buildpacks included. To use, specify buildpacks at build time
• paketobuildpacks/builder-jammy-full - Ubuntu 22.04 Jammy Jellyfish full image with buildpacks for Apache HTTPD, Go, Java, Java Native Image, .NET, NGINX, Node.js, PHP, Procfile, Python, and Ruby
• paketobuildpacks/builder-jammy-tiny - Tiny base image (Ubuntu Jammy Jellyfish build image, distroless-like run image) with buildpacks for Java, Java Native Image and Go
• paketobuildpacks/builder-ubi8-base - Ubi 8 base builder with buildpacks for Node.js, Java, Quarkus and Procfile

The Paketo buildpacks in the README are still current, but I would propose to change the builder for Google to gcr.io/buildpacks/builder:latest, and for Heroku to heroku/builder:24.

Additional consideration:

The default value for CNB_PLATFORM_API might need to be bumped from 0.9 to 0.14. The latest 0.15 appears not yet to be supported by all builders.