Ability to choose header date / day of the week format

Problem/Motivation

By default, the days of the week are printed in full (Monday, Tuesday, etc...). This can eat up lots of horizontal space, makes days of the week different lengths, and can make styling difficult.

Ideally, we should have a simple way to choose the date format to Mon, Tue, Wed, etc...

Steps to reproduce

Create view using 'Calendar by month' format.
Load in content with date data.
In 'Month' settings, choose date field.
Save view.

See that each day of the week is in a long form: Monday, Tuesday, Wednesday, etc...

Proposed resolution

In 'Month' settings, add an option to choose the shortened 3-letter version of days of the week.

In PHP date format, this is 'D': https://www.php.net/manual/en/datetime.format.php