Allow up local detection by operator

[dofinn]

Description of the change:
When operator-sdk up local is called. Set OPERATOR_UP_LOCAL=true

Motivation for the change:
When developing locally, it would be convenient to detect this in
the actual operator code so things like metrics can be bypassed.

With the OPERATOR_UP_LOCAL=true, operators can skip certain
bootstrapping tasks like attempting to register with a metrics service
while still maintaining logic for registering failures in production.

An example can be seen below:

	// detect if operator-sdk up local is run
	detectLocal := os.Getenv("OPERATOR_UP_LOCAL")

	// Configure metrics. If it errors, log the error and exit
	if detectLocal != "true" {
		if err := metrics.ConfigureMetrics(context.TODO(), *metricsServer); err != nil {
			log.Error(err, "Failed to configure Metrics")
			os.Exit(1)
		}
	}

[dofinn]

/retest

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[AlexNPavel]

This is actually already implemented. It's used to disable metrics and leader election on local mode runs, but I suppose it could be used by the user as well, we just don't have it documented. When using up local, we set OSDK_FORCE_RUN_MODE=local: https://github.com/operator-framework/operator-sdk/blob/master/cmd/operator-sdk/up/local.go#L142

[joelanford]

Since this is already implemented, I'm going to close this PR.

IMO, we should not document this and should instead advocate that users that need more advanced control of various go commands that are wrapped by operator-sdk should instead use a Makefile and implement their own logic in custom targets. See #1600 (comment) for more background.

[dofinn]

@joelanford @AlexNPavel Thank you for taking the time to enlighten me on this.

Seems like this is a suitable thing to document, why hide it? If you are going to advocate users to edit their own Makefile, I would recommend at least adding that to the FAQ: https://github.com/operator-framework/operator-sdk/blob/master/doc/faq.md