The plugin should be disabled when WP Rocket is enabled

[CrochetFeve0251]

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Describe the bug
We should disable rll when wpr is enabled.

That leads to the lazyload script being loaded twice.

We could also display a warning message telling them that the plugin has no usage when wpr is here.

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Additional context
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Acceptance Criteria (for WP Media team use only)
Clear instructions for developers, to be added before the grooming