MRG: Migrate report to Jinja2

[hoechenberger]

Closes #943

Merge checklist

Maintainer, please confirm the following before merging:

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

[codecov]

Codecov Report

Merging #944 (b66a162) into main (d618c46) will decrease coverage by 0.39%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##             main     #944      +/-   ##
==========================================
- Coverage   94.79%   94.39%   -0.40%     
==========================================
  Files          23       25       +2     
  Lines        3495     3550      +55     
==========================================
+ Hits         3313     3351      +38     
- Misses        182      199      +17     

Impacted Files	Coverage Δ
mne_bids/report/_report.py	85.71% <85.00%> (ø)
mne_bids/report/__init__.py	100.00% <100.00%> (ø)
mne_bids/report/templates/participants.jinja	100.00% <100.00%> (ø)

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