Allow enum name to differ from column name

[emilong]

I found that while migrating some existing Rails enum columns to str_enum, I wanted a way to have str_enum "take over" the old enum name and generated methods while pointing at a new column so I could keep both columns for a smooth transition.

To that end, I added another option to str_enum called :column where you can specify the column explicitly.

It doesn't seem to have created any regressions as far as I can tell from the test suite or require a major version bump.

Hoping this might be useful for other folks too!

[swrobel]

This seems really valuable as we're evaluating moving our existing enums to str_enums. It seems like it's been a while since this was opened, but thoughts on merging @ankane?