Add missing mass flow rate units

[hopkins-tk]

Proposed change

Add missing mass flow rate and concentration units.
To be used in subsequent PR to Aseko Pool Live to change units to standard ones.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
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• The code change is tested and works locally.
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[home-assistant]

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[joostlek]

This PR is changing our entity model. Before we can review this PR there needs to be approval in a discussion in our architecture repository.

https://github.com/home-assistant/architecture/discussions

https://developers.home-assistant.io/docs/core/entity#changing-the-entity-model

[joostlek]

Note, you can still continue working on the aseko pool one, but this change can't be merged without a proposal