Move event list to a YAML file

[sebbASF]

It's easier to maintain a YAML file than parts of a large HTML file.

ALso, once there is a central event resource (e.g. Google Calendar with extra details) it will be easy to update the source of the data.

The changed data can be seen at:

https://www-sebb-events.staged.apache.org/#upcoming-events

[loganloganlogan]

Hi Sebb, we are researching a more wholesale change to how events are handled on the website, so will put this one on hold for the time being.

[rbowen]

Hey, @sebbASF, I was wondering if there might be a way to merge this into how we do stuff on events.apache.org to make it more attractive, reduce data/work duplication, and finally get off of the Google Calendar dependency? I'd want to run that by @markt-asf first, of course, since he's usually the one that updates the event calendar and a new workflow might be a little additional work for him. What do you think, Mark?

[markt-asf]

I'm fine with updating a YAML file rather than a Google calendar. I assume that is all that would required and CI would then build and update the site?

[sebbASF]

This PR merely extracts the data from the HTML page and puts it in YAML.
When the site is rebuilt, the YAML is loaded into variables which are passed to the page template to create the page.
So yes, once the YAML file is changed, the site will be updated automatically.

As to combining:

Would the list of events be the same for apache.org as well as events.a.o?
[It might be possible to filter the YAML before passing it to the template]

Who would be responsible for updating the content?
At present each site has separate owners; they would need to agree on how changes are made.

[sebbASF]

Using an external YAML should make it possible to ignore events that are in the past.
At present manual editing is needed

Note that the templating system used on this site can use data from various sources, so the event list would not have to be stored locally (this site is rebuilt regularly even if no updates are made to the sources).

[rbowen]

I expect that events.a.o would list a larger set of events than the a.o site, and we could accomplish this with tagging of some kind.

This is all very unformed brainstorming, but has been on my list for a long time, and I just saw this PR.