Timestamps for the kitty video

[waikoo]

Originally discussed in #6281, this pull request adds timestamps under the introductory kitty video.

Its purpose is to give a better overview in navigating and comprehending the video.

Timestamps can be edited and expanded upon using timestamps_source.js and the ARRAY object in timestamps.js to get styling.
A separate stylesheet is used with the timestamps namespace to differentiate itself from other parts of the code.
conf.py is modified to include the new files needed to generate the new element and to specify the script being a module to be able to use a separate source file (timestamps_source.js).

To mitigate potential security vulnerabilities associated with using innerHTML and similar methods, this pull request intentionally creates and manipulates elements dynamically through JavaScript, ensuring a safer and controlled approach to adding timestamps under the introductory kitty video.

Additionally, this implementation ensures seamless functionality in both light and dark modes, providing a consistent user experience across different viewing environments.

Thanks to @kovidgoyal for the guidance.