Inferring public ip address automatically

_This issue was originally opened by @LazzariPaolo in https://github.com/hashicorp/packer/issues/11420 and has been migrated to this repository. The original issue description is below._

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AWS builders require whitelisting the public ip address of the machine which is running the build.
E.g:

`temporary_security_group_source_cidrs = ["213..."]`

it would be nice to be able to avoid having to hardcode this in the template, and instead get this info automatically, perhaps with a function.

Something like:

`temporary_security_group_source_cidrs = [local_public_ip]`