Add monthfiled to resolve strings fields

[Siedlerchr]

Fixes #13375

Steps to test

Open JabRef settings -> Entry -> Resolve strings for -> montfiled is present

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• [/ Screenshots added in PR description (if change is visible to the user)
• [/] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [/] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

One more thing: Isnt monthfield an alias for month? Isn't it then an issue regarding aliassed fields?

[koppor]

One more thing: Isnt monthfield an alias for month? Isn't it then an issue regarding aliassed fields?

OMG, its filed; not field. Thus, no alias

[Siedlerchr]

One more thing: Isnt monthfield an alias for month? Isn't it then an issue regarding aliassed fields?

OMG, its filed; not field. Thus, no alias

Yes! That's a tricky one. Had to carefully read the issue... 😆

[koppor]

With nice preference migration. Thank you!

I removed duplicate "mothfiled" in 4f1e64a (#13379)

[trag-bot]

@trag-bot didn't find any issues in the code! ✅✨