Load ElectrodesTable metadata when loading ElectricalSeries from NWB file

[wulfdewolf]

This PR adds the metadata in the ElectrodesTable as TsdFrame metadata when loading a ElectricalSeries from a NWB file using load_file.

Before we only looked for "label", since that is an example in pynwb.
However, it seems that neuroconv uses "channel_name".
There doesn't seem to be a standard for the columns in the ElectrodesTable.

The solution I came up with was to make the TsdFrame column names the index of the ElectrodesTable and then add all the columns of the ElectrodesTable that do not have object as type as metadata columns in the TsdFrame.
This way things like location are also loaded.

Addresses #586

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
pynapple/io/interface_nwb.py	83.17% <100.00%> (+0.87%)	⬆️
pynapple/io/loader.py	52.50% <ø> (ø)

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