feat: replace edX® certificate icons

[Cup0fCoffee]

Description

Fixes openedx/platform-roadmap#425

This PR replaces the icons for the certificates. Old certificates icons contained edX trademark logos, which were not suitable for the open source repos. Replaced with icons that contain Open edX logos.

[openedx-webhooks]

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[sarina]

@Cup0fCoffee I invited you to the Triage group in Open edX so that tests will run for you :) please accept the invite :))

[sarina]

Also I am not a committer for frontend repos so I've requested a review from @brian-smith-tcril - Brian, this is approved by product and looks fine to me but want second 👀

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.20%. Comparing base (24c9437) to head (2fc9083).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1687   +/-   ##
=======================================
  Coverage   90.20%   90.20%           
=======================================
  Files         343      343           
  Lines        5747     5747           
  Branches     1381     1381           
=======================================
  Hits         5184     5184           
+ Misses        546      544    -2     
- Partials       17       19    +2     

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