Dedicated LTI navigation for educators

[ayub02]

• Added a top-level Learning Tools Interoperability (LTI) section to the educator documentation.
• Organized LTI documentation by integration direction.
• Separated LTI tools used in course content from tools shown in course navigation.
• Moved existing LTI component and Open edX provider documentation into the new hierarchy.
• Added a guide for configuring an LTI discussion provider.
• Rewrote and relocated the Course Live guide.
• Added contextual links from the existing Discussions and Learner Engagement documentation.
• Reordered the main educator navigation.
• Updated relevant screenshots and maintenance tables.

Co-author: Codex

[sarina]

As discussed on Slack, I'll review this Monday morning as I think you wanted to make a few more changes. Please tag me when it's ready!

[ayub02]

@sarina this is ready for review.

[sarina]

Said in DM but adding here:

I'm going to merge this to get it in, but I think the LTI stuff does need to be elevated on the Educator's pages (I really don't think as many people use the sidebar as you do, given how I've seen people interact with the docs site on screenshares). With this change, LTI pages are now only available via sidebar navigation.

I'll merge and then play around with it a bit.