feat: update certificate icons

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

src/courseware/course/course-exit/CourseCelebration.jsx

@@ -18,8 +18,8 @@ import { getAuthenticatedUser } from '@edx/frontend-platform/auth';
 
 import CelebrationMobile from './assets/celebration_456x328.gif';
 import CelebrationDesktop from './assets/celebration_750x540.gif';
-import certificate from '../../../generic/assets/edX_certificate.png';
-import certificateLocked from '../../../generic/assets/edX_locked_certificate.png';
+import certificate from '../../../generic/assets/openedx_certificate.png';
+import certificateLocked from '../../../generic/assets/openedx_locked_certificate.png';
 import { FormattedPricing } from '../../../generic/upgrade-button';
 import messages from './messages';
 import { useModel } from '../../../generic/model-store';

src/courseware/course/course-exit/ProgramCompletion.jsx

@@ -4,7 +4,7 @@ import PropTypes from 'prop-types';
 import { getConfig } from '@edx/frontend-platform';
 import { FormattedMessage, useIntl } from '@edx/frontend-platform/i18n';
 import { Alert, Button, Hyperlink } from '@openedx/paragon';
-import certImage from '../../../generic/assets/edX_certificate.png';
+import certImage from '../../../generic/assets/openedx_certificate.png';
 import messages from './messages';
 
 /**

src/courseware/course/sequence/lock-paywall/LockPaywall.jsx

@@ -9,7 +9,7 @@ import {
 import { Locked } from '@openedx/paragon/icons';
 import SidebarContext from '../../sidebar/SidebarContext';
 import messages from './messages';
-import certificateLocked from '../../../../generic/assets/edX_locked_certificate.png';
+import certificateLocked from '../../../../generic/assets/openedx_locked_certificate.png';
 import { useModel } from '../../../../generic/model-store';
 import { UpgradeButton } from '../../../../generic/upgrade-button';
 import {