Update release schema to be coherent with merging specification

[kindly]

As mentioned in #284 a compiledRelease in an OCDS record has the same schema as a standard OCDS release.
However, some of the fields, most notably the release ID and date, make no sense once compiled and they are also mandatory. This means it is not possible to make a compiled release that makes sense and validates.

The best approach would be to make a new sightly modified version of the OCDS release to take this into account. Naming possibly merged-release-scema.json

[duncandewhurst]

It's also worth noting that whilst the merging rules guidance states that the id and date fields should be omitted from a compiled release, the example data on the same page of the docs shows a compiled release with both of these fields included.

We should fix this as when we update the docs as part of the upgrade

[Bjwebb]

@kindly Your current code drops tag from the versioned release. I'm not quite clear that this is the correct behaviour.

[Bjwebb]

Just discussed with @kindly why dropping tag does make sense, because every versioned block has the associated releaseTag.

[jpmckinney]

The issues that @kindly and @duncandewhurst reported haven't been fixed.