pkg/ui: add first stage of redesigned tracez page

[benbardin]

Begins to implement

https://www.figma.com/file/LUptGAxt5x1idq6eZLA50o/BulkIO-Traces?node-id=59%3A7958

When complete, the new pages will offer:

• A robust route structure and full redux integration for better navigation.
• Denser information display.
• More information display, i.e. start time/duration, and expanding mutliple tag groups.
• A new span details page, which will include child span information.

For now, this page is behind a new route with no entrypoint. It implements the core route structure, redux selectors and API calls. Left for later PRs are Take Snapshot, the Span Details page, pagination, search filtering, and View Raw JSON.

Release note: None

[cockroach-teamcity]

This change is 

[benbardin]

Hey David! Could you help specifically with typescript review? (If there's other stuff you want to talk too about I'm game!) Thank you!

[benbardin]

bors r+

[craig[bot]]

Build succeeded:

• Bazel Essential CI (Cockroach)