Update ProjectFormGroup to use PJ component and remove unnecessary style classes

The following discussion from !84846 (merged) should be addressed:

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

  Question (non-blocking): Any reason to not use gl-link here as well? Would help automatically add the noopener noreferrer part. Though I see that it links to an internal link so we shouldn't be using target=_blank in the first place.

  Also a nit but the help-link class looks redundant.

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

  Nit (non-blocking): I tried it locally and removing all of these classes produces the exact same UI, i.e. this is redundant. The only modifier that has any effect is text-primary which IMO should just be removed as we shouldn't encourage different colors (just this component has 2 links which have different colors).

Implementation plan

in app/assets/javascripts/confidential_merge_request/components/project_form_group.vue , update/refactor the styling like suggested above.