ingest/pipeline: update LedgerBackends to be InboundAdapters

[sreuland]

What problem does your feature solve

no clear path on how to use network tx meta as the source of origin in a data transformation pipeline using ingest/pipeline sdk per #5400

What would you like to see?

• update ledgerbackend.LedgerBackend to become an InboundAdapter from the new ingest/pipeline sdk:
  *. LedgerBackend.Publish(ctx context.Context, outboundChannel Channel)
  • update the LedgerBackend implementations to implement Publish method, Allows the backend to be run as an async worker routine, until its ledger range is satisfied or forever if unbounded range. It will run a loop to obtain each LedgerCloseMeta internally via GetLedger(), and serialize and send it as Message to pipeline on outboundChannel, thus, provides the origin Event for application pipelines
    • ledgerbackend.BufferedStorageBackend
    • ledgerbackend.CaptiveStellarCore

Depends on #5400

What alternatives are there?

[sreuland]

after processors lib design review, we decided to go with a different approach of pipelines created from observable streams using functional operators, this infra not needed and obsoleted by #5412.