Fix backward compatibilty issues

[turmelclem]

Content

• fix AggregatorCapabilities struct with a default value to ensure backward compatibility
• fix E2E test backward compatibility by putting back the version of backend cardano-db used to avoid default version mecanism

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested
• Documentation
  • Update README file (if relevant)
  • Update documentation website (if relevant)
  • Add dev blog post (if relevant)
  • Add ADR blog post or Dev ADR entry (if relevant)
  • No new TODOs introduced

Issue(s)

Closes #2730

[github-actions]

Test Results

    4 files  ±0    164 suites  ±0   23m 54s ⏱️ -7s
2 195 tests ±0  2 195 ✅ ±0  0 💤 ±0  0 ❌ ±0 
6 760 runs  ±0  6 760 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 0a8945f. ± Comparison against base commit d7ce977.

♻️ This comment has been updated with latest results.

[jpraynaud]

LGTM 👍