Add multi-arch build target

[rooftopcellist]

Please confirm the following

• [X] I agree to follow this project's code of conduct.
• [X] I have checked the current issues for duplicates.
• [X] I understand that AWX Operator is open source software provided for free and that I might not receive a timely response.

Feature Summary

A new docker-buildx make target should be added to support multi-arch builds of the awx operator.

Context - https://github.com/ansible/eda-server-operator/issues/158

[jon-nfc]

PR Inbound.

related to #31