DAST MR widget link should be replaced with a button

Problem to solve

This MR widget should use a download button in place of the Download scanned resources link shown below:

Proposal

TLDR: Update both buttons to the Small button component

In order to provide users with a consistent experience while interacting with the security merge request widget, all similar actions within the subgroup headers (e.g. SAST, DAST, Coverage fuzzing, etc.) should utilize the same Pajamas Components.

For this specific issue, the Small button component is likely the best candidate to align on since it will ensure all of the subgroup headers remain a consistent size and allows for the security widget's primary actions (e.g. View full report & Expand/Collapse) to maintain their prominence.

In addition to updating the button styles, the download icon used on the Coverage fuzzing button should also be removed. As stated in the Pajamas documentation for dropdown buttons:

The chevron is the only icon that should be present with a text label.

Current State	Proposed State

Proposal Update

There were some changes to the Design during UX-Review for consistency reasons !63407 (comment 594698779)

proposal update

Implementation Plan

• Update DAST widget
  • Replace GlLink with GlButton component in grouped_security_reports_app.vue
  • Add size attribute as sm
• Update Coverage Fuzzing Widget
  • Remove icon attribute from security_report_download_dropdown.vue
  • Update size attribute as sm

cc @derekferguson