Add secret command
Adds faas-cli secret command for managing secrets via the OpenFaaS CLI/API @viveksyngh @leodido @LucasRoesler @alexellis
Changelog:
- Implement pinned template repo clone #576 by @LucasRoesler
- Add secret list command to faas-cli #578 by @viveksyngh
- Add faas secret remove command #579 by @alexellis
- Add create command for secrets #580 by @viveksyngh
- Add faas secret update command #582 by @leodido