[REF] Events: Restructure docs before adding new content

[fw-bot]

Reorganized the Events docs for clarity and structure. Most changes consist of moving existing pages into folders, although some in-line changes were made to fix broken references, doc links, image attachments, etc.

Changelog

• Moved applications/marketing/events/create_events.rst and applications/marketing/events/event_templates.rst into new applications/marketing/events/event_setup/ folder
• Moved applications/marketing/events/sell_tickets.rst, applications/marketing/events/event_booths.rst, and applications/marketing/events/event_sponsors.rst into new applications/marketing/events/promote_monetize/ folder
• Moved applications/marketing/events/event_tracks.rst and applications/marketing/events/track_manage_talks.rst into new applications/marketing/events/attendee_experience folder
• Created toctree pages for attendee_experience/, promote_monetize/, and event_setup/ folders.
• Various in-line edits across the affected docs to fix broken refs.
• Updated 18.0 redirect rules file to fix broken links.

Version Scope
This 18.0 PR should be FWP up to master.

Forward-Port-Of: #17193

[robodoo]

[fw-bot]

@stepperpig cherrypicking of pull request #17193 failed.

stdout:

Auto-merging redirects/18.0.txt
CONFLICT (content): Merge conflict in redirects/18.0.txt

Either perform the forward-port manually (and push to this branch, proceeding as usual) or close this PR (maybe?).

you can use git-fw to re-do the forward-port for you locally.

⚠️ after resolving this conflict, you will need to merge it via @robodoo.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port