No expiry on mocks

[notjaywu]

Close INS-4164

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
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[jackkav]

Closed in favour of setting a very long expiry, would be interested in passing 0 or no number translating to no expiry rather than removing the feature.