Add event metadata handling

[thht]

PR Description

So far, mne-bids only uses event_id to handle events. However, we really like and use the event metadata functionality of MNE Python. So, here is an update that you can also use event metadata as an alternative.

Merge checklist

Maintainer, please confirm the following before merging.
If applicable:

• All comments are resolved
• This is not your own PR
• All CIs are happy
• PR title starts with [MRG]
• whats_new.rst is updated
• New contributors have been added to CITATION.cff
• PR description includes phrase "closes <#issue-number>"

[welcome]

Hello! 👋 Thanks for opening your first pull request here! ❤️ We will try to get back to you soon. 🚴🏽‍♂️

[sappelhoff]

Hi @thht, I just had a quick glance and it already looks very clean and reasonable!

Please also follow the steps described here (in particular a changelog item with a high level description of your addition):

https://github.com/mne-tools/mne-bids/blob/main/CONTRIBUTING.md#instructions-for-first-time-contributors

And tag me for a review once you are ready 🙏

[thht]

@sappelhoff Thanks for the quick reply!

As you can see, I added the authors, citation and changelog information. I also fixed the docs issue.

Failing tests should be due to the bids-validator issue you already reported in #1287.

So, I think, this one is ready for review!

[codecov]

Codecov Report

Attention: Patch coverage is 97.10145% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.45%. Comparing base (87eea28) to head (5544cd4).
Report is 59 commits behind head on main.

Files	Patch %	Lines
mne_bids/write.py	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1285      +/-   ##
==========================================
- Coverage   97.61%   97.45%   -0.16%     
==========================================
  Files          40       40              
  Lines        8685     8779      +94     
==========================================
+ Hits         8478     8556      +78     
- Misses        207      223      +16     

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[sappelhoff]

I am very happy with this, thanks a lot!

[welcome]

🎉 Congrats on merging your first pull request! 🥳 Looking forward to seeing more from you in the future! 💪