Update existing POCs to CDEvents v0.4

[afrittoli]

CDEvents has two POCs in https://github.com/cdfoundation/sig-events/tree/main/poc.
Those two POCs:

• are hosted in the sig-events repo
• use an old version of the golang SDK
• have somewhat sparse documentation
• are not discoverable through cdevents.dev

This issue is about fixing all these.
It would be ok to split it in sub-issues if needed.

[e-backmark-ericsson]

See also the small related comment here: cdfoundation/sig-events#128 (comment)

[afrittoli]

@rjalander is this something you intend to work on / contribute to?

[afrittoli]

We might use the POC to test mixed CDEvents versions as well.

[rjalander]

Yes @afrittoli, we have in our backlogs to work on this Updating PoC version to use CDEvents v0.1