Add reference {REF...} support for otp field

Summary

Some services use Symantec VIP, and when that is generated, it can work for multiple services. It would be helpful to put a reference in the otp custom attribute to the entry for Symantec so I only need to update one otp entry if things need changing.

Examples

Right now, it seems the otp uses the {REF} string as the secret, and doesn't follow the field reference.

Context

(see Summary above)