services/horizon/internal/txsub: Check transaction submission results using repeatable read transaction

[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 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

Check transaction submission results using repeatable read transaction.
Fixes #2628

Why

We make two DB queries: first checking if tx result exists in a DB (ResultByHash), second getting the current sequence number of a source account (GetSequenceNumbers):

Queries are not sent in a transaction (REPEATABLE READ) so it's possible that ResultByHash and GetSequenceNumbers are getting data for different ledgers: one without a tx ingested, second with tx ingested which can result in bad_seq errors.

Because we are using Horizon DB only I think we should remove ResultProvider and SequenceProvider interfaces and use history.Q directly to send queries.

Known limitations

Previously, when we wrapped horizon endpoints in repeatable read transactions this resulted in some performance degradation. We will need to test that production load does not overwhelm the horizon db.

[bartekn]

Let's add a short comment explaining why this has to be done in a repeatable read tx. And let's error.Wrap all errors in this function.