[FEAT] Course navigation opens LTI links

[ivynya]

Is your feature request related to a problem? Please describe.
LTI (external tools) attached at the course level are displayed inside the course navigation component, but currently do nothing.

Describe the solution you'd like
Clicking this sidebar element should launch the LTI / external tool in a new window. This should be done with the Canvas external tools API, which is already partially integrated into Caravel at src/app/core/services/canvas/course/course.service.ts

Additional context
URL: caravel-next.sdbagel.com/courses/:courseId
Component: src/app/course/course-nav/

Would you like to contribute this feature?
This is a Hacktoberfest issue - new contributors are welcome! If you have any questions about the code, structure, or contributing to Caravel, feel free to ask.