closes https://github.com/coder/internal/issues/464
# Summary
This PR resolves a flaky test that was sensitive to DST transitions in
various time zones. The root of the flake was:
* a bug; the query and its tests assume 24 hours per day
* the tests used local system time, which resulted in failures for dates
proximal to DST transitions
# Changes
Query:
The original query assumed 24 hour intervals between each day, which is
not a valid assumption. It now increments `1 day` at a time.
Database tests:
Database level tests for the query all assumed 24 hour days. They now
increment in DST-aware days instead. Instead of using time.Now() as a
base for testing, the test uses a series of dates over the course of an
entire year, to ensure that DST transition dates are present in every
test run.
# API Endpoint
The endpoint that delivers the user status chart now accepts an IANA
timezone name as a parameter and passes it, keeping the existing offset
as a fallback, to the database query.
API level tests were added to ensure the correct response form and error
behaviour. Correctness of content is tested at the database level.