[WIP] Add GTN Event pages

[shiltemann]

Enable creating event pages in the GTN. These pages are very similar to learning paths, but with support for times and practical info etc.

@teresa-m these event pages can be used for Galaxy Academy, will help you set that up when I am done with this PR.

Course Overview	Program

TODOs

• [x] support custom sessions (such as breaks, non-GTN tutorials, etc)
• [x] add index page that lists all current and upcoming events
• [x] add setup instructions (galaxy server, TIaaS, Slack/support invite and channel)
• [ ] import previous events from video-library repo as tests of feature-completeness
• [x] RSS feed for Hub (and others)
• [x] support draft: true on events
• [x] add jsonld event metadata (thanks @hexylena)
• [ ] create contributing tutorial about how to define events
• [ ] add news item announcing event support
• [ ] announce newly added events via GTN news bot
• [x] show list of upcoming events on GTN homepage?
• [x] support external events (e.g. organizers have their own event page, but want to list it on GTN for dissemination)
• [x] schema and linting
• [ ] a way to indicate that the program is not finalized and subject to change
• [x] separate schema validation for external events (layout event_external)
• [ ] support for multiple tracks in a program
• [ ] support for smorgasbord-like CYOA programs?
• [ ] support simply pointing to learning pathways for a program?

Stretch Goals:

• [ ] On tutorials that are being used, add a banner of "This is being taught in an upcoming course, sign up here"
• [ ] On topic pages show a box if any courses are teaching materials from a given topic
• [x] Copy button that copies a slack/toot formatted version (with emoji for cost/when/deadlines/etc)
• [ ] Automatically use archive links for past events?
• [ ] Google form to add event PR

[teresa-m]

@shiltemann Thanks a lot for taking care of this. I am more than happy to help. Not sure how much I can be of help with the technical part but providing content for a tutorial or copiying one of the old events guess I could help with. Just tell me if you think I could be helpfull with some tasks.

[hexylena]

https://www.ebi.ac.uk/training/events/single-cell-rna-seq-analysis-using-galaxy-2022/ just as possible design reference, I think they did some nice things (splitting out important content to not be overwhelming, good CTAs like "register" and "program")

[hexylena]

https://docs.google.com/document/d/1qLbSgJmXA0xnuXaQl4gTvH0IR5K4sHNcGXsOQS5AMno/edit#heading=h.vfgxyghkwcri is the reference for TeSS metadata that can be parsed

[hexylena]

example old toot/post

# Take from page.excerpt
It will once again be free, online, self-paced, and choose-your-own-adventure style. It will feature all the content of previous editions, plus lots more!
The preliminary program can be found on the course website.  (Several modules are still in development, so check back regularly for the updated program!)

:date: May 22-26, 2023 # need to write a function to do this concise formatting
:arrow_right: https://gxy.io/smorgasbord3 # GTN url, or gxy.io/GTN:E00001 if page.short_id available
:writing_hand: Registration is now open! (url)

[shiltemann]

Thanks @teresa-m! yes, once this technical part is done, would be great if you could have a look and provide feedback, and start trying to put the Smorg/Academy schedule in and let me know where things are missing or confusing or not working as expected etc :)