Add policy instrument functions #1826

[l-emele]

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[stap-m]

To fix this, you should use characteristic of and has characteristic, instead of has fuction and has bearer. See also https://github.com/OpenEnergyPlatform/ontology/issues/1826#issuecomment-2320326168

[l-emele]

Thanks for your suggestions, @stap-m . It seems to work now and I'll set this PR as ready for review.