feat: add CLICKHOUSE_ROLE support

[anatoly-anatoly]

Add support for CLICKHOUSE_ROLE environment variable

Summary

This PR adds support for the CLICKHOUSE_ROLE environment variable, allowing users to specify a role for authentication when connecting to ClickHouse.

Changes

• Added CLICKHOUSE_ROLE to the list of optional environment variables in mcp_env.py.
• Updated ClickHouseConfig to include a role property.
• Updated get_client_config to pass the role to the ClickHouse client settings.
• Added unit tests in tests/test_config_interface.py to verify the configuration.

Usage

"env": {
  "CLICKHOUSE_ROLE": "my_role"
}

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