Add support for EventDetection with channel index

[stephprince]

Motivation

Fix #2068. Adds support for nwb-schema changes to EventDetection in NeurodataWithoutBorders/nwb-schema#620

How to test the behavior?

See updated example in the ecephys tutorial.

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running ruff check . && codespell from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.90%. Comparing base (87dcadc) to head (d35ecf1).

Files with missing lines	Patch %	Lines
src/pynwb/ecephys.py	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           nwb-schema-2.9.0    #2091      +/-   ##
====================================================
- Coverage             94.93%   94.90%   -0.03%     
====================================================
  Files                    28       28              
  Lines                  2802     2809       +7     
  Branches                716      719       +3     
====================================================
+ Hits                   2660     2666       +6     
  Misses                   87       87              
- Partials                 55       56       +1     

Flag	Coverage Δ
integration	74.61% <28.57%> (-0.12%)	⬇️
unit	84.65% <85.71%> (+<0.01%)	⬆️

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[rly]

Looks good. Let's merge the schema PR, update the submodule in this repo, and then merge this PR to the 2.9.0 branch.