ingest/ledgerbackend: Add ledger backend which replays ledgers

[tamirms]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've reviewed the changes in this PR and if I consider them worthwhile for being mentioned on release notes then I have updated the relevant CHANGELOG.md within the component folder structure. For example, if I changed horizon, then I updated (services/horizon/CHANGELOG.md. I add a new line item describing the change and reference to this PR. If I don't update a CHANGELOG, I acknowledge this PR's change may not be mentioned in future release notes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Close #5480

Following #5556 , this PR implements a ledger backend which takes synthetically generated ledgers, merges them with real ledgers, and then replays them at a configurable rate.

Why

This ledger backend will be used to benchmark ingestion duration for horizon / rpc when ingesting ledgers with a high volume of soroban transactions. These benchmarks will inform us of horizon and rpc's ceiling when it comes to ingestion throughput.

Known limitations

[N/A]

[tamirms]

@karthikiyer56 I think I have addressed your code review feedback, could you take another look?

[2opremio]

All my comments are optional. I am mostly concerned about the role of the passed ledger backend, which is a bit unintuitive to me.