Use ECMWF's downstream-ci in GitHub Actions

[iainrussell]

What maintenance does this project need?

To make earthkit's ci work in the same way as other ECMWF packages, the following should be done:

• add to downstream-ci as per instructions here
• dependencies in the tree for now should be earthkit-data and earthkit-maps; earthkit-meteo can be taken from PyPi for now
• any ci actions that are special to this package should be in a separate yml file
• revise the cd action as per instructions here
• Note: this cannot be done until the same is done for earthkit-data (Use ECMWF's downstream-ci in GitHub Actions earthkit-data#259) and earthkit-maps (Use ECMWF's downstream-ci in GitHub Actions earthkit-maps#33).

Thank you!

Organisation

ECMWF