Replace vue-resource with axios in groups_service.js

This is part of &1281 (closed).

We want to get rid of vue-resource in app/assets/javascripts/groups/service/groups_service.js (any occurrence of Vue.http / this.$http needs to be replaced with axios).

added to epic &1281 (closed)

added [deprecated] Accepting merge requests backstage [DEPRECATED] frontend labels

I'm going to attempt to jump on these. Thank you @winh :)

changed milestone to %12.3

added Community contribution workflowin dev labels and removed [deprecated] Accepting merge requests label

assigned to @leetickett and @winh

added devopsmanage label

mentioned in merge request !32420 (merged)

added workflowin review label and removed workflowin dev label

mentioned in commit e8c58d62

closing this because https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/32420 was merged

removed workflowin review label

closed