Update iron-air assumptions to be more conservative

[tgilon]

This PR needs the #172 to be merged first.

Changes proposed in this Pull Request

This PR proposes to improve iron-air assumptions (introduced in #149) using the same specification sheet as before, but using the upper bound instead of the midpoint for investment costs. We propose using 20$/kWh for instead of the previous 17.5$/kWh. The round trip efficiencies, fixed O&M costs and learning rates remain unchanged. They are all taken from the same specification sheet.

The values are manually converted to EUR 2023 and filled in the inputs/manuals_inputs.csv. The workflow updates them to EUR 2020.

Assumptions

• All assumptions are taken from the specification sheet.
• A premium of US$100/kW is assumed for Europe. Currently, this is also assumed for US data. This PR requires the Create dedicated US inputs #172 to be merged first.
• The assumed exchange rate is 1EUR = 1.05 USD.

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Data source for new technologies is clearly stated.
• Newly introduced dependencies are added to environment.yaml (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the GPLv3 license.

[tgilon]

FYI @daniel-rdt