fix(#0086): replace date time dropdowns with select elements

[SigifredoChaconB]

Description

Replaces the custom Bootstrap dropdown components in the Display Date & Time module with native select elements to maintain consistency with the rest of the admin tool UI.

Changes include:

• Replaced custom Bootstrap dropdown for date format selection with a native select element bound to dateFormatSelection via ngModel
• Replaced custom Bootstrap dropdown for datetime format selection with a native select element bound to dateTimeFormatSelection via ngModel
• Removed unused dropdown LESS styles and replaced with width selectors for the native select elements
• Removed date parameter from onDateFormatSelected and onDateTimeFormatSelected since ngModel handles the value update directly
• Updated unit tests to reflect the new select elements and simplified method signatures

Code review checklist

• Readable: Concise, well named, follows the style guide, documented if necessary.
• Tested: Unit and/or e2e where appropriate
• Internationalised: All user facing text

License

The software is provided under AGPL-3.0. Contributions to this project are accepted under the same license.

[jomcarvajal]

LGTM