feat: Syllabus page for learner MFE

[xitij2000]

This PR implements a plugin for the Learner MFE that adds a course tab that displays the syllabus.

syllabus-tab-demo.mp4

Testing instructions

• Use the version of the learner MFE that includes the slots this plugin needs: feat: Add slots to add tab links and add mechanism for plugin routes openedx/frontend-app-learning#1645
• Install this plugin using npm install --no-save https://github.com/open-craft/frontend-plugin-syllabus-tab.git#kshitij/syllabus-tab
• Use the following contents in env.config.jsx:

  import { pluginSlots, PLUGIN_ROUTES } from '@open-craft/frontend-plugin-syllabus-tab';
  
  const config = {
    PLUGIN_ROUTES: [
     ...PLUGIN_ROUTES,
    ],
    pluginSlots: {...pluginSlots},
  };
  
  export default config;

[pkulkark]

Just the note about the block cache issue here, otherwise LGTM 👍

• I tested this: Verified that the syllabus tab shows up and functions as expected.
• I read through the code
• Includes documentation