Calendar view: second try

[yshmarov]

Description

Calendar view. Based on https://github.com/avo-hq/avo/pull/2727

Monthly calendar currently implemented. We can consider other resolutions in the future.

Records are displayed in calendar by default by created_at, but this can be overriden in the resource with self.calendar_view

Date is stored in params => refreshing page will not lose current period

TODO:

• [ ] styling
• [ ] week, day, month view? (not just "calendar"?)
• [ ] use a better calendar icon
• [ ] tests
• [ ] ~event duration~
• [x] user can select starts_at attribute
• [x] user can format title
• [ ] group events that start at the same time

@adrianthedev 's requirements:

• [x] a read-only view of events
• [x] events shown in order on a day cell (if they have a time)
• [ ] events that can span over a longer period of time - in the first iteration I do not want to include duration

Fixes # (issue)

Checklist:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works

Screenshots & recording

Manual review steps

1. Step 1
2. Step 2

Manual reviewer: please leave a comment with output from the test if that's the case.