Add the pass-through of generator event information for EDM4hep

[tmadlener]

BEGINRELEASENOTES

• EDM4hep Input / Output: Add the passing through of generator event information for EDM4hep, fixes Add GeneratorInfo to EDM4hepReader #1373

ENDRELEASENOTES

Keeping this as draft for now, until we have finalized all the details upstream, but I think those should be largely transparent for these changes.

[github-actions]

Test Results

   18 files     18 suites   7h 0m 42s ⏱️
  372 tests   372 ✅ 0 💤 0 ❌
3 278 runs  3 278 ✅ 0 💤 0 ❌

Results for commit 2ac7695.

♻️ This comment has been updated with latest results.

[tmadlener]

I realized that the ingestion of the GeneratorEventParameters was tied to the presence of an EventHeader, which shouldn't be the case. I have also added pre-processor version checks for EDM4hep to make CI pass for older EDM4hep versions.