Add settings to enable 24-hour time format and customizable date format

[GimleLarpes]

Description

Based on #1739 and #2344 Options for configuring date and time formats have long been requested (see #60 and duplicates). This PR aims to add this functionality.

This PR adds:

• A "Date & Time" subsection in General settings
• A toggle that allows the user to switch between 12-hour and 24-hour time formats
• A dropdown/text input field to let the user select a date format

As requested in #60.

In addition to the current D MMM YYYY format the following options are added: DD/MM/YYYY, MM/DD/YYYY, YYYY/MM/DD, Custom - where the user can enter a 16-character dayjs format string.

Example image:

Fixes #60

Type of change

• [o] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected) (new function params)
• [o] This change requires a documentation update

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[GimleLarpes]

Could this get reviewed @ajbura ?

[github-actions[bot]]

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[GimleLarpes]

I've now added a hint for the formatting. I would've preferred to prevent overflow using flexFlow: 'column wrap' or something similar, but the current method works. I've also added 24hr functionality to the TimePicker.