Add install.sh Script, Streamline README, and Modularize GitHub Actions Workflow

[chiukapoor]

Updates

• Create a script for installing the KubePlus operator and KubePlus kubectl plugin
• Update README.md to include a "Quick Installation" section and move the getting-started example to a separate file to streamline the README
• Update GitHub Actions PR workflow to use the install.sh script for installing the KubePlus operator and kubectl plugin
• Modularized GitHub Actions PR workflow into distinct steps
• Moved CI to use kind instead of minikube for better speed

Issue

• Fixes: https://github.com/cloud-ark/kubeplus/issues/1349

[devdattakulkarni]

Looks good!