Add explicit post method to device provision call.

[rtibbles]

Summary

Cleanup from #6969 - the device provision call was relying on rest JS' implicit POST behaviour when data is submitted, this adds the explicit POST method to fix device provisioning.

Reviewer guidance

Can you provision the device?

Fixes #7030

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Reviewer Checklist

• Automated test coverage is satisfactory
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• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[jredrejo]

Thanks, I have checked if fixes the issue