feat: [FC-0044] Course unit - Copy/paste functionality (#884)

Implement copy/paste.

Co-authored-by: monteri <36768631+monteri@users.noreply.github.com>
Co-authored-by: ihor-romaniuk <ihor.romaniuk@raccoongang.com>

src/__mocks__/clipboardUnit.js

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+export default {
+  content: {
+    id: 67,
+    userId: 3,
+    created: '2024-01-16T13:09:11.540615Z',
+    purpose: 'clipboard',
+    status: 'ready',
+    blockType: 'vertical',
+    blockTypeDisplay: 'Unit',
+    olxUrl: 'http://localhost:18010/api/content-staging/v1/staged-content/67/olx',
+    displayName: 'Introduction: Video and Sequences',
+  },
+  sourceUsageKey: 'block-v1:edX+DemoX+Demo_Course+type@vertical+block@vertical_0270f6de40fc',
+  sourceContextTitle: 'Demonstration Course',
+  sourceEditUrl: 'http://localhost:18010/container/block-v1:edX+DemoX+Demo_Course+type@vertical+block@vertical_0270f6de40fc',
+};

src/__mocks__/clipboardXBlock.js

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+export default {
+  content: {
+    id: 69,
+    userId: 3,
+    created: '2024-01-16T13:33:21.314439Z',
+    purpose: 'clipboard',
+    status: 'ready',
+    blockType: 'html',
+    blockTypeDisplay: 'Text',
+    olxUrl: 'http://localhost:18010/api/content-staging/v1/staged-content/69/olx',
+    displayName: 'Blank HTML Page',
+  },
+  sourceUsageKey: 'block-v1:edX+DemoX+Demo_Course+type@html+block@html1',
+  sourceContextTitle: 'Demonstration Course',
+  sourceEditUrl: 'http://localhost:18010/container/block-v1:edX+DemoX+Demo_Course+type@vertical+block@vertical1',
+};

src/__mocks__/index.js

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+export { default as clipboardUnit } from './clipboardUnit';
+export { default as clipboardXBlock } from './clipboardXBlock';