[Config] Add --config=FILE argument

[ccgsnet]

Summary

Introduces a JSON-based configuration file for DAS services and a --config=FILE CLI argument for bus_node and bus_client. Configuration is merged so that CLI-provided values override the config file.

Changes

• JsonConfig – Wrapper over the parsed JSON with schema version and path-based access (at_path("atomdb.redis.port")), plus get_or<T>(default) for optional values.
• JsonConfigParser – Loads and parses the config file (with optional validation).
• config/example.json – Example config covering atomdb (Redis, MongoDB, MorkDB, remote peers), agents/endpoints, and ports.

CLI integration

• bus_node and bus_client accept --config=FILE. If omitted, the default config path is used.
• Config and CLI are merged: any option passed on the command line overrides the value from the config file.

Wiring

• bus_node uses the config for service endpoints, ports, atomdb type, Redis/MongoDB/MorkDB settings, and remote AtomDB peers.
• RemoteAtomDB and Properties are updated to consume the new config (including remote_peers and related fields).

Tests

• config_parser_test – Unit tests for the JSON config parser (path lookup, get_or, schema, etc.).
• remote_atomdb_test – Adjusted to work with the new config-based setup.

Notes

• Existing behaviour is preserved when no config file is present or when using the default path with sensible defaults.
• The Bazel/Docker permission workaround in MODULE.bazel (rules_kotlin archive_override) is out of scope for this PR and can be handled separately.