Fixing ColorScheme serialization

[brimoor]

Fixes ColorScheme serialization by using the same ID field pattern used by Label classes.

The existing logic did not satisfy the following requirement, which, for example, was causing the @voxel51/utils/edit_dataset_info operator to be unable to understand custom color schemes.

import fiftyone as fo

color_scheme = fo.ColorScheme()
d = color_scheme.to_dict(extended=True)

# previously raised an error; now succeeds
also_color_scheme = fo.ColorScheme.from_dict(d, extended=True)

assert color_scheme == also_color_scheme

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6086bf2) 15.99% compared to head (cc894e5) 15.99%.
Report is 2 commits behind head on release/v0.23.6.

Additional details and impacted files

@@               Coverage Diff                @@
##           release/v0.23.6    #4092   +/-   ##
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  Coverage            15.99%   15.99%           
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  Files                  732      732           
  Lines                82062    82062           
  Branches              1110     1110           
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  Hits                 13123    13123           
  Misses               68939    68939           

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[benjaminpkane]

LGTM. @lanzhenw can confirm