Add a group summary element, stories and tests

[sultan-duisenbay]

Added a group summary element as in the screenshot -

Added the element, story and tests.

The element is not embedded in the code

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chases2, sultan-duisenbay

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/GoogleCloudPlatform/testgrid/blob/master/OWNERS)~~ [chases2,sultan-duisenbay] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[sultan-duisenbay]

Improved the test according to the comment. Thanks @chases2 !

/hold cancel