Fix container restart issues in local mode

[leighmcculloch]

What

Fix several issues that prevent the quickstart container from restarting cleanly in --local mode with persistent data, either data saved in a volume or a stopped and restarted container.

Changes:

1. Skip Soroban config upgrades if already applied - Add sentinel file check (.upgrade-config-initialized) to upgrade_local() to skip config upgrades on restart
2. Skip friendbot init if already initialized - Add sentinel file check (.quickstart-initialized) to init_friendbot() to prevent re-initialization on restart

Why

When the container restarts with --local and a persistent ledger:

• Soroban config upgrades fail because the root account has sourced prior transactions and the hardcoded account sequence is out-of-date
• Friendbot init was running on every start and isn't idempotent, overwriting configuration on each restart corrupting the config file

These failures would trigger service shutdown, making the container non-restartable without removal.

Close #896

[Copilot]

Pull request overview

This PR adds idempotency to Soroban config upgrades in the quickstart container's --local mode by introducing a sentinel file check. The change prevents upgrade transactions from re-running on container restart, which was causing failures because these upgrades can only succeed when the root account has no prior transactions.

Changes:

• Added a sentinel file check (.upgrade-config-initialized) to skip Soroban config upgrades if they've already been applied
• Wrapped the upgrade logic in an if/else block that checks for the sentinel file before running upgrades

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