Add revive linter and enable superfluous-else rule

[RebeccaMahany]

Adds https://github.com/mgechev/revive -- https://github.com/mgechev/revive/blob/master/RULES_DESCRIPTIONS.md#superfluous-else

Example error message:

% golangci-lint run      
cmd/launcher/main.go:78:11: superfluous-else: if block ends with call to panic function, so drop this else and outdent its block (revive)
			} else {
				level.Debug(logger).Log("msg", "Nothing new")
			}

[zackattack01]

🔥 🚀