"ssl_certificates" and "certificate_manager_certificates" are mutually exclusive

[rodriguezsergio]

My local copy of this repo at this commit fails during a Terraform plan when I define a value for https_proxy_config.certificate_manager_certificates.

This PR fixes that in not only net-lb-app-int, but a few other directories.

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

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[juliocc]

Closing this since it's been inactive for 2 weeks. Feel free to reopen when ready.