Update to latest JSON schema version(s)

[Athanasius]

We're still specifying and using JSON schema v4, which is working for us.

But check if there's any reason to move to the latest / not be on this old version.

[klightspeed]

It looks like the major breaking changes in 2019-09 and 2020-12 include:

• definitions is renamed to $defs
• id is renamed to $id

[robbyxp1]

If it affects the clients, lets not.

[Athanasius]

If it affects the clients, lets not.

It shouldn't affect them at all.

There is no requirement in any EDDN documentation for any Sender or Listener to be performing validation of the messages versus the schemas.

Both of those changes @klightspeed outlined are only in the Schema files, not the actual EDDN messages based on them.

But, yes, we'd obviously give a heads up in case Senders/Listeners are performing validation at all themselves. It wouldn't just be a "oh yeah, we're now using this newer version of the JSON Schema standard, deal with it".

Note also that, in theory, it would all be automatic because the version of the JSON Schema spec used in the Schemas is explicitly linked to. Any validation should be picking that up rather than assuming a specific version itself.

Any Sender or Listener perforrming validation already needs to do due diligence on keeping in sync with the live branch schemas/ directory anyway, else they're going to run into problems.

And, yes, I'll have to remember to update my own Listener's copy of schemas ;) .