services/horizon/internal/actions: populate default cursor value for history endpoints

[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

The following endpoints use a TOID cursor value derived from the ledger sequence number:

/effects
/operations
/transactions
/ledgers
/trades
/payments

When a cursor is omitted the query to fetch the history data will look like:

select * from history_transactions order by id asc (if the order is asc which is by default))

or

select * from history_transactions order by id desc (if the order is desc)

However, the query performs better with a paging clause, eg:

select * from history_transactions where id >= 200076760811839488 order by id asc

This commit sets a default cursor value based on the paging order. If order is set to asc, we will use the oldest ledger -1 to create the default cursor value. Similarly, if the order is set to desc, we will use the latest ledger + 100 to create the default cursor value.

Known limitations

We obtain the oldest and latest ledger using ledgerState *ledger.State which is refreshed periodically. It is possible that ledgerState is out of date but that is why we add a buffer of 100 extra ledgers to ledgerState.CurrentStatus().HistoryLatest.

[urvisavla]

LGTM! Nice solution to addresses the issue of 503 timeouts for ASC. The same default cursor logic isn't required for DESC but I'm assuming there's no downside to using it for DESC as well.

[tamirms]

@urvisavla good point regarding the order=desc behavior. I've decided to restore the original behavior for desc to limit the footprint of this PR

[sreuland]

looks good, left one minor comment for consideration.