update resources/webinars section - details section

add content to details sections of all webinar pages,

go through the video or the presentation slides and summarise what was presented.
- title of presentation
- background of presentation
- main concepts
- conclude with discussion topics brought up

one sentence or two for each point above is okay
if there are multiple presentations, make individual paragraphs for each presentation

Start in the resources/webinars section and inspect each webinar page's details section, then review the associated video or presentation slides mentioned in the issue. Add a separate summary for each presentation covering its title, background, main concepts, and discussion topics; completion means all webinar pages have these details filled in.

Written by the indexing model from the issue text.