write provisioned certificate to "active-certificate.pem.crt"

[RogerZhongAWS]

Motivation

• create a static filepath that gets overwritten upon a successful retry of the Fleet provisioning workflow.
• QoL for specific applications on the device that may need the x509 certificate to reside at a guaranteed location.

Modifications

Change summary

• extracted logic into a private function for calling it twice. First time with certificate ID and second time with the "active" prefix

Testing

• manually tested /w FP template

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