exp/services/captivecore: Captive Core API fixes

[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

Close #3228
Close #3229

This commit correctly sets the log level in the captive core api logger. With this fix the captive core api logs are now visible and formatted correctly.

This commit also marks the active request as invalid whenever a captive core function returns an error. By marking the active request as invalid we ensure that the captive core subprocess is recreated the next time POST /prepare-range is invoked.

Known limitations

[N/A]