feat: Add plugin slots for sidebars (#1752)

src/plugin-slots/CourseAuthoringUnitSidebarSlot/README.md

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+# CourseAuthoringUnitSidebarSlot
+
+### Slot ID: `course_authoring_unit_sidebar_slot`
+
+### Plugin Props:
+
+* `courseId` - String.
+* `blockId` - String. The usage id of the current unit being viewed / edited.
+* `unitTitle` - String. The name of the current unit being viewed / edited.
+
+## Description
+
+The slot wraps the sidebar that is displayed on the unit editor page. It can
+be used to add additional sidebar components or modify the existing sidebar.
+
+## Example
+
+![Screenshot of the unit sidebar surrounded by border](./images/unit_sidebar_with_border.png)
+
+The following example configuration surrounds the sidebar in a border as shown above.
+
+```js
+import { PLUGIN_OPERATIONS } from '@openedx/frontend-plugin-framework';
+
+const config = {
+  pluginSlots: {
+    course_authoring_unit_sidebar_slot: {
+      keepDefault: true,
+      plugins: [
+        {
+          op: PLUGIN_OPERATIONS.Wrap,
+          widgetId: 'default_contents',
+          wrapper: ({ component }) => (
+            <div style={{ border: 'thick dashed red' }}>{component}</div>
+          ),
+        },
+      ],
+    },
+  }
+};
+export default config;
+```

src/plugin-slots/CourseAuthoringUnitSidebarSlot/index.tsx

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+import { getConfig } from '@edx/frontend-platform';
+import { PluginSlot } from '@openedx/frontend-plugin-framework/dist';
+import TagsSidebarControls from '../../content-tags-drawer/tags-sidebar-controls';
+import Sidebar from '../../course-unit/sidebar';
+import LocationInfo from '../../course-unit/sidebar/LocationInfo';
+import PublishControls from '../../course-unit/sidebar/PublishControls';
+
+export const CourseAuthoringUnitSidebarSlot = (
+  {
+    blockId,
+    courseId,
+    unitTitle,
+  }: CourseAuthoringUnitSidebarSlotProps,
+) => (
+  <PluginSlot
+    id="course_authoring_unit_sidebar_slot"
+    pluginProps={{ blockId, courseId, unitTitle }}
+  >
+    <Sidebar data-testid="course-unit-sidebar">
+      <PublishControls blockId={blockId} />
+    </Sidebar>
+    {getConfig().ENABLE_TAGGING_TAXONOMY_PAGES === 'true' && (
+    <Sidebar className="tags-sidebar">
+      <TagsSidebarControls />
+    </Sidebar>
+    )}
+    <Sidebar data-testid="course-unit-location-sidebar">
+      <LocationInfo />
+    </Sidebar>
+  </PluginSlot>
+);
+
+interface CourseAuthoringUnitSidebarSlotProps {
+  blockId: string;
+  courseId: string;
+  unitTitle: string;
+}