Fix(modules): configlet_build_config documentation issue for the prefix parameter

Issue Summary

cf https://github.com/aristanetworks/ansible-avd/pull/1946#discussion_r923976345

Basically in one place the prefix is optional and in another place it is required (module doctsring documentation)

This should be aligned properly

Which component(s) of AVD impacted

arista.avd.configlet_build_config

How do you run AVD ?

Ansible CLI (with virtual-env or native python)

Steps to reproduce

No response

Relevant log output

No response

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