Open #15208 within the org (#15310)

* Add cypress tests for reference/metrics/:id page

* Add metrics/:metricId/edit route

* Use router location for metric's isEditing state

Data Reference keeps `isEditing` state flag in Redux store (it's shared across metrics, segments and DB references)

Metrics page now uses router's path name to distinguish reading and editing states

* Use non-Redux callbacks at MetricDetailContainer

* Add missing prop type definition

* Fix editing callbacks not passed to MetricDetail

* Fix signInAsAdmin test utility usage

* Reorder imports

* Use cy.findByText instead of cy.contains

* Fix Metrics data reference test

For some reason, when running Cypress tests,
the page appears in `cannot read property fields of undefined`
However it works correctly when running Metabase locally

Checking for undefined `fields` explicitly fixes the problem
Anyway, most likely this component is going to be removed in #15209

* Fix metrics test

Co-authored-by: Anton Kulyk <kuliks.anton@gmail.com>