services/horizon/internal/ingest: Add more fine-grained reap metrics

[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

Add duration metrics for reaping of lookup tables where we can see how much time is spent reaping each table. See link below which displays the new metrics on staging:

https://grafana.stellar-ops.com/d/x8xDSQQIk/stellar-horizon?orgId=1&viewPanel=2531

Also, add metrics which count how many rows were deleted from each lookup table. See link below which displays the new metrics on staging:

https://grafana.stellar-ops.com/d/x8xDSQQIk/stellar-horizon?orgId=1&viewPanel=2541

Why

These fine-grained metrics are required so that we can analyze which tables are the most expensive to reap.

Known limitations

[N/A]