exp/services/ledgerexporter: Initial draft

[urvisavla]

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 updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• 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

see README.md

[Shaptic]

First pass review! Looks really solid so far! And even has some test coverage 🤌

Have we given any thought to parallel uploads? I'm not sure if it would necessarily provide a performance benefit and it would have a significant add'l complexity, but I'm curious if the idea has discussed.

[urvisavla]

Have we given any thought to parallel uploads? I'm not sure if it would necessarily provide a performance benefit and it would have a significant add'l complexity, but I'm curious if the idea has discussed.

By parallel uploads do you mean simultaneously uploading to multiple destinations or concurrently exporting multiple ledger ranges? The former can introduce complexity but the latter can be achieved by running multiple instances of ledger exporter, each handling a distinct range. Currently, the ledgerexporter design doesn't restrict multiple instances from running but the only consideration is the machine capacity to run multiple captive-cores on the same system.

[Shaptic]

This is really really well-designed, great work so far @urvisavla! 👏 I need some more time to digest the interactions between the channels but here's a smattering of misc. comments for now.

[tamirms]

great job 🎉 !