Move history archive to /opt/stellar for persistence

[leighmcculloch]

What problem does your feature solve?

The local history archive is written to /tmp/stellar-core/history/vs, which is not persisted when mounting /opt/stellar for persistent mode. This means history archive data is lost across container restarts, even when users have configured persistence.

What would you like to see?

Move the history archive to /opt/stellar/history-archive/data (or similar path under /opt/stellar) so it persists alongside other data when users mount the /opt/stellar directory.

This would be consistent with how the meta-archive is being configured in #870.

What alternatives are there?

Users could manually configure volume mounts for /tmp/stellar-core/history/vs, but this is non-obvious and inconsistent with the documented persistence approach of mounting /opt/stellar.