🐛 pkg/log/zap: use enabled in UseDevMode, add tests

[joelanford]

This PR fixes a bug where func UseDevMode(enabled bool) always sets the Development option to true, regardless of the value of enabled.

This PR also adds tests for the New() function and the Opts-related functions.

[k8s-ci-robot]

Hi @joelanford. Thanks for your PR.

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[DirectXMan12]

/lgtm
/approve

thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: DirectXMan12, joelanford

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