orchestrator: run FreeBank as a Core fork again, with its own wallet

[mblowes]

FreeBank is a Bitcoin Core 0.16 fork again. It keeps its own wallet, and its boot is pinned to the eCash fork block.
Stop and the sync probe send the cookie to a Core fork, so shutdown no longer waits the full grace period.
BitWindow shows the FreeBank state, balance and settings button. This PR also holds the work from #2393.

[mblowes]

Rebased onto 0514e5f. That commit added migrations/023_chains_config.json and config version 23 for the GitHub downloads, so this PR's FreeBank patch is now migrations/024_chains_config.json, and all three chains_config.json copies are at version 24. Upstream's 023 is unchanged. Only the commit that adds the migration changed in the rebase; the other five applied cleanly. Locally: go build, go vet and golangci-lint are clean, the three chains_config.json copies are identical, and chains_config_migration_test.dart passes.

About the failing "validate all openapi_schema snapshots" check: only truthcoin fails. truthcoin-dc v0.18.0 (released 09-22) no longer matches the snapshot refreshed in a665a9d against 0.17.0. Any PR that touches sidechain-orchestrator/sidechain/** will hit it, and this PR doesn't touch truthcoin. Refreshing it with TRUTHCOIN_SCHEMA_UPDATE_CLI=1 makes it pass locally, but it's your snapshot to update. Also, since 0514e5f the Rust chains download bare daemons, so that job may no longer find the *-cli binaries it runs.