Distinguish exploration step types with icons (#6368)

* Distinguish exploration step types with icons

- Add an icon for pageview groups, pageviews, and 'No further action', each with a tooltip
- Capitalize 'No further action' label
- Fix search input spacing
- Change grid column width to 19rem

* Remove pageview and `No further action` icons and update CR formatting

* Update tests

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Co-authored-by: Adrian Gruntkowski <adrian.gruntkowski@gmail.com>