Update checkbox to toggle for keep latest artifacts

The following discussion from !119068 (merged) should be addressed:

• @pgascouvaillancourt started a discussion: (+1 comment)

  This LGTM 💯

  I do have a concern about the UX of the Keep artifacts from most recent successful jobs option though:

  

  The design system says that a checkbox should not be used when:

  • only one option in a set can be selected
  • you are wanting to have a change immediately applied when an option is selected

  Both those guidelines are being violated here as it's a single option, and the value is stored to the DB whenever the checkbox is toggled. We should probably consider using a GlToggle component instead.

  This MR did not introduce this checkbox though, so this concern is definitely out of scope, but I'd like to make sure we are tracking this somewhere. @gdoyle do you know if there's already an issue for this?

Proposal

Update the checkbox to a toggle: replace the GlFormCheckbox component with a GlToggle, see this nearby toggle for reference