Enhanced version command to check for latest version and warn user

[vishal-biyani]

• Check and notify user if the latest release available
• Refactor Get K8s Version func to avoid unnecessary call

Example:

$ ./cli version
{"Version": "dev", "GitCommit": "none", "BuildDate": "unknown"}
There is a new version of kbrew available: v0.0.4, please run 'kbrew update' command to upgrade

[vishal-biyani]

I am not sure if this is working, I just tried with my CLI and I think we have a new version released now?

kbrew version
{"Version": "v0.0.4", "GitCommit": "02d07c49185c10cfebb4bcbbb55e93eb3a2181e7", "BuildDate": "2021-05-13T04:02:47Z"}