[dagit] Roots for Pipelines, Settings
Create root pages for /workspace/pipelines and /settings, which are intended as top-level navigation items.
- /workspace/pipelines will show a flattened list of all pipelines in the loaded workspace. It's a simple table to start with, and we can decide which columns are best suited for it.
- /settings consolidates /flags and timezone settings, and gives us a place to add more user-specific settings in the future.
Test Plan: Navigate to these routes in dagit, verify success.
Reviewers: bengotow, alangenfeld, cdecarolis
Reviewed By: bengotow
Differential Revision: https://dagster.phacility.com/D6231