chore: Add support for linting using golangci-lint

[kevdowney]

Is this a BUG REPORT or FEATURE REQUEST?:
CHORE
What happened:
Need to start linting the codebase
What you expected to happen:

• Add a makfile target to download and run golangci-lint
• Add a github action to run linter as a pr gate.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• Addon Manager version
• Kubernetes version :

$ kubectl version -o yaml

Other debugging information (if applicable):

• Addon status:

$ kubectl describe addon <addon-name>

• controller logs:

$ kubectl logs <addon-manager-pod>