Closes #18936: add color name support for cable bulk import

[Jathn]

Closes: #18936

The changes made allows for colors to be imported as either hex code or with the label name.

Changes made:

• Make "color" a custom field instead of using the built in Django field. It now allows longer names for the colors (previously only 6 chars matching that of a hex code.)
• The given color is matched against the labels of ColorChoices. In case of a hex code, the behavior is the same as previous implementation and all test cases still pass.
• The exception raised if the color is over six characters and not in ColorChoices is now separate from that of the base case.

Note: It seems that color choices in general are limited to the set defined in ColorChoices, however I can't seem to find these documented anywhere. Didn't include it as it is out of scope for this issue.

[arthanson]

Thanks @Jathn !