Document the value behind "Default" for the Custom Link "Button Class"

[maddin8]

Change Type

Addition

Area

Customization

Proposed Changes

I would like to propose that aside from the possible non-default values for "Button Class"/"button_class" of Custom Links, documentation is updated to include the information that the value displayed as "Default" in the Netbox UI is actually called "outline-dark". "Default" is as well included in CSV exports of Custom Links from already populated instances, which makes it harder for non-experienced users to determine what value to provide when mass-importing Custom Links with a button_class of "Default"(/"outline-dark").

I originally raised this in #15596 which hopefully provides enough reason why I think this should be included in the documentation.

[maddin8]

Updated formatting of the table in the second commit.

[jeremystretch]

It would not be appropriate to duplicate all these entries in the written documentation. Instead, the field definition under the CSV import form should include a help button which displays the available choices, as exists for similar fields. (button_class should be defined on the form as a CSVChoiceField.)

@maddin8 do you want to try this?

[jeremystretch]

Reclassified this as a bug, as the import form field is not of the correct type.