PersonsModal has no results for day interval due to timezones

[benjackwhite]

Bug description

We have a bug with the calculation of ranges for people

1. Bug Part 1: Creating a trends time range uses the date_from value of your local time - not the start of whatever range in question (usually the day). This means depending on what time you create the trend, you get different results
2. Bug Part 2: The response part for persons_urls is bucketed by day but with the project timezone offset which results in weird values like

GET /api/projects/2/actions/people/?...
   &date_from=2022-08-20T22:00:00+00:00
   &date_to=2022-08-20T22:00:00+00:00
   &interval=day

3. This overall affects Trends in general in that the relative transformations (last N days) include one day too many in both directions. With specific date ranges the day in the future is missing but the extra day in the past is still there.

May be related to #11352 and #9565

How to reproduce

1. Set your project timezone to a non-utc value (e.g. +2 hours Berlin)
2. Create a new Trend (beware of cached results!) with a Day breakdown
3. Click the line to open the PersonsModal to see no results (or fewer than expected

Environment

• PostHog Cloud
• self-hosted PostHog, version/commit: please provide

Additional context

1. The timezone for the response is correct from the perspective of date_from (we want to be offset for the project's timezone) but the mixture of identical date_to and interval=day makes it unclear what the response is loading. I think it ends up taking the date_from and rounding to the end of the day in utc.

Thank you for your bug report – we love squashing them!