Add migration for FLH change in hydrogen production nodes #1609
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This PR adds a migration to accommodate the FLH change of LH2 regasifiers & LOHC reformers in quintel/etsource#3287 & https://github.com/quintel/etdataset/pull/1046.
Goes together with:
https://github.com/quintel/etdataset/pull/1046
quintel/etsource#3287