Add screenshot plugin (#217)

source/plugins/screenshot/tests.yml

@@ -0,0 +1,12 @@
+- name: Screenshot plugin (default)
+  uses: lowlighter/metrics@latest
+  with:
+    token: NOT_NEEDED
+    plugin_screenshot: yes
+    plugin_screenshot_url: https://github.com
+    plugin_screenshot_title: Test
+    plugin_screenshot_selector: body
+    plugin_screenshot_background: no
+  timeout: 1800000
+  modes:
+    - action