Add a user menu with login, logout to UI

[ChristopherChudzicki]

What are the relevant tickets?

Closes #241

Description (What does it do?)

This PR adds a user menu in top-right corner with log in / log out links as appropriate. A few other links are added, too.

Authenticated user / Anonymous user *Note, "Learning Paths" only available to those with editing permissions".

/

Additionally, I made some updates to the reusable SimpleMenu component.

How can this be tested?

Prerequisites: Connect your local instance to keycloak; either local keycloak or on RC. Ask me for creds if you need them.

Assuming you are initially unauthenticated:

1. Unauthenticated: Visit http://localhost:8063/ ; in top right, click user menu and log in. You should be redirected to keycloak, after which you're redirected back to MIT Open.
2. Authenticated: Now click usermenu
   • if your user has is_learning_path_editor permission, they'll see a "Learning Paths" link.
   • all authenticated users see "Log out" link.
3. Authenticated: Try logging out. It should work.
   • Note: Does not currently redirect to MIT Open

Some accessibility stuff: This is most easily tested as a superuser, since you'll have multiple links int he dropdown usermenu.

• Check that you can tab to the usermenu trigger and open it with keyboard
• Once it's open, check that navigation with keyboard arrows works.
  • The indidividual menu items are navigable with keyboard arrows, NOT via tab. See https://www.w3.org/WAI/ARIA/apg/patterns/menubar/
• The whole menu item should be clickable as a link
  

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (eab21e3) 76.80% compared to head (a39dee6) 76.86%.
Report is 4 commits behind head on main.

❗ Current head a39dee6 differs from pull request most recent head 79fd138. Consider uploading reports for the commit 79fd138 to get more accurate results

Files	Patch %	Lines
...omponents/src/components/SimpleMenu/SimpleMenu.tsx	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #319      +/-   ##
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+ Coverage   76.80%   76.86%   +0.05%     
==========================================
  Files         281      282       +1     
  Lines       13047    13097      +50     
  Branches     2133     2141       +8     
==========================================
+ Hits        10021    10067      +46     
- Misses       2800     2803       +3     
- Partials      226      227       +1     

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[collinpreston]

Nicely done. Works well with screen reader.