services/horizon: Add feature flag to reuse Captive-Core storage dir

[bartekn]

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

Adds a new --captive-core-reuse-storage-dir flag to enable/disable Captive-Core storage dir reuse.

Why

In Stellar-Core 17.1.0 there is a bug that can potentially corrupt storage dir: stellar/stellar-core#3085. The feature flag can be enabled or removed when a fix is released.

[paulbellamy]

Would it be better to detect the version of core, and use that?

[bartekn]

Would it be better to detect the version of core, and use that?

We are still not sure which Stellar-Core version will include a fix.