Add package standardflags for -automaxprocs commandline argument

[nixpanic]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test

/kind feature

/kind flake

What this PR does / why we need it:

The new -automaxprocs flag can be used to set the GOMAXPROCS environment variable to match the configured Linux container CPU quota.

Which issue(s) this PR fixes:

Related: kubernetes-csi/node-driver-registrar#495

Special notes for your reviewer:

Applications can call EnableAutomaxprocs() to enable it during startup.

Does this PR introduce a user-facing change?:

The AddAutomaxprocs() function adds the -automaxprocs boolean flag to the commandline options. By default the flag is disabled.

[nixpanic]

/cc jsafrane

[xing-yang]

What are the requirements for using this flag properly?

[nixpanic]

What are the requirements for using this flag properly?

The flag only has effect when the container where the application runs has CPU limits configured.

The maxprocs package reads the CPU quota from cgroups under /sys/... and sets the GOMAXPROCS environment variable based on the CPU quota. If CPU quota is not configured, or not supported, the flag does not have any effect.

[xing-yang]

/lgtm

[jsafrane]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jsafrane, nixpanic

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