fix pressure level metadata

[cosunae]

Purpose

When using interpolate_k2p with 50 hPa as parameters, the output written in grib comes with wrong metadata (by factor 100)
23 typeOfFirstFixedSurface = 100 [Isobaric surface (Pa) (grib2/tables/11/4.5.table) ]
24 scaleFactorOfFirstFixedSurface = 0
25-28 scaledValueOfFirstFixedSurface = 500000

The problem is, I think, that the derived key "level" is interpreted as hPa

Code changes:

• Modify the coordinates so that 'z' is represented in hPa

Checklist

Before submitting this PR, please make sure:

• You have followed the coding standards guidelines established at Code Review Checklist.
• Docstrings and type hints are added to new and updated routines, as appropriate
• All relevant documentation has been updated or added (e.g. README)
• Unit tests are added or updated for non-operator code
• New operators are properly tested

Additionally, if the PR updates the version of the package

• The new version is properly set
• A Tag will be created after the bump

Review

For the review process follow the guidelines at Checklist

[cfkanesan]

Can you provide a reproducible example?

[cfkanesan]

I think it's fine to default to hPa as a unit for the pressure levels but please set the typeOfLevel to isobaricInhPa