[Tagging] Tag sections, subsections, and the whole course

[bradenmacdonald]

"As a course author, I want to apply tags to my course as a whole."

"As a course author, I want to apply tags to sections and subsections."

Figma: Course tags and Section/Subsection Tags

Acceptance criteria:

• On the course outline page of the Course Authoring MFE, make Sections and Subsections display their tag count if they have tags. The count should be clickable and open the tagging drawer.
• Put "Manage Tags" into the "three dots" menu for sections and subsections.
• When changes are saved in the tagging drawer, the counts shown on the course outline should be instantly refreshed (via React-query invalidation).
• Course tag count and "manage tags" link for the course as a whole is at the top of the page, as shown in Figma. It also opens the tagging drawer and will also instantly reflect updates once saved.

No need to modify the legacy courseware page; this is MFE only.