feat(Labels): Various UI/UX improvements

[grafakus]

✨ Description

Related issue(s): resolves https://github.com/grafana/explore-profiles/issues/88 and more

A couple of UI/UX improvements for the "Labels" exploration type:

• The "Select" action has been removed on panels with a single label value (further breakdown does not make sense)
• The "Compare" action has been removed when there's only a single panel in the grid (nothing to compare to)
• Bar gauges for single label values are not helpful (see https://github.com/grafana/explore-profiles/issues/88), they have been replaced by Stats visualizations, e.g.:
• The "Bar gauge" button on the panel type switcher has been renamed to "Totals" (works for when the UI displays bar gauge or stat panels)

📖 Summary of the changes

See diff tab for specific comments

🧪 How to test?

• See related issue + manual testing in local after checking out this PR's branch

[github-actions[bot]]

Unit test coverage

Lines	Statements	Branches	Functions
	12.54% (470/3746)	9.85% (138/1400)	9.48% (108/1139)