docs: add link to interactive demo

[salaxander]

Add a link to the newly created Killercoda interactive demo!

Closes #346

[salaxander]

@sozercan - killercoda account name has been updated, this should be good to go now

[sozercan]

@salaxander can we add a CI for this to make sure it's working, and if not, we'll get some sort of signal in the future?

another concern i have is that, this'll need to be updated. For example, looking at https://github.com/killercoda/scenarios-opa/blob/main/intro/assets/gatekeeper.yaml#L760 it has an ancient version of GK which won't be updated. We'll need some sort of update mechanism, perhaps similar to copa-action where it gets the latest release from Github.

[salaxander]

I think we can make the update work with actions, but I don't have a clue how we'd do an availability check beyond pinging the URL and getting a 200 back

[sozercan]

@salaxander i meant this part of it: https://github.com/project-copacetic/copa-action/blob/main/action.yaml#L36-L41
This will automatically pull in the latest release instead of being hardcoded

[salaxander]

@sozercan I recently updated the script to pull in the latest release of Copa

[sozercan]

@salaxander can we add a simple nightly or weekly github action to execute the scripts so we'll know if it's broken