Mark EventStore based I/O as deprecated

[tmadlener]

BEGINRELEASENOTES

• Introduce deprecation warnings for the EventStore based I/O model as it will be removed in favor of the Frame based one

ENDRELEASENOTES

In order to pass CI deprecation warnings are temporarily accepted and this exception has to be taken back again when the EventStore code is removed.

[tmadlener]

The edm4hep workflow currently fails because it still uses the EventStore until key4hep/EDM4hep#184 is merged. I suggest we wait for that to go in first, and the merge this.

[hegner]

@tmadlener - before merging we have to get the Gaudi part fixed as well.

[tmadlener]

In principle this can be merged even without those fixes since we are only introducing a few deprecation warnings and not yet removing anything. But since this is not extremely urgent we can also wait.

[hegner]

@tmadlener - actually it is errors in the current setup. Otherwise the PR checks would succeed ;-)

[tmadlener]

The errors are deprecation warnings that are triggered in the EDM4hep build. They should be fixed by key4hep/EDM4hep#194 and key4hep/EDM4hep#182

[tmadlener]

All downstream (EDM4hep) fixes have been merged, so I think this could be merged.