[cmd/mdatagen] Add warnings in resource_attributes section

[dmitryax]

Author of metadata.yaml should be able to specify the same warnings in resource_attributes section as available in the metrics section. This is needed to provide a graceful way to handle changes to default/optional resource_attributes.

[github-actions]

Pinging code owners for cmd/mdatagen: @dmitryax. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[abhide]

@dmitryax I would like to work on this issue. Can you please assign it to me?

[dmitryax]

Thanks, @abhide . Assigned to you

[github-actions]

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• cmd/mdatagen: @dmitryax

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