Make None colum in Fuels_data optional

Description

Fix TDR to load Fuels_data.csv even without a None column.

Addresses #552

[x] Code changes are sufficiently documented; i.e. new functions contain docstrings and .md files under /docs/src have been updated if necessary.
[x] The latest changes on the target branch have been incorporated, so that any conflicts are taken care of before merging. This can be accomplished either by merging in the target branch (e.g. 'git merge develop') or by rebasing on top of the target branch (e.g. 'git rebase develop'). Please do not hesitate to reach out to the GenX development team if you need help with this.
[x] Code has been tested to ensure all functionality works as intended.
[x] CHANGELOG.md has been updated (if this is a 'notable' change).
[X] I consent to the release of this PR's code under the GNU General Public license.

By running any example case with TimeDomainReduction: 1 and without a None column in the Fuels_data.csv input file.

After the PR is approved

[x] Check that the latest changes on the target branch are incorporated, either via merge or rebase
[x] Remember to squash and merge if incorporating into develop