[C++][FlightRPC][ODBC] Enable DSN default values on macOS

[alinaliBQ]

Describe the enhancement requested

Acceptance Criteria:

1. Enable these DSN default values for ODBC on macOS:

• useEncryption
• useSystemTrustStore
• disableCertificateVerification

2. Remove setting default in ReadDsnString since the driver manager on Windows and Mac, Linux implements SQLGetPrivateProfileString differently, so the way of passing defaults is consistent across platforms.
3. Document default values

---

Example code for enabling default values:

arrow/cpp/src/arrow/flight/sql/odbc/odbc_impl/flight_sql_connection.cc

Lines 211 to 221 in 2fcc3ec

	bool FlightSqlConnection::GetUseWideChar(const ConnPropertyMap& conn_property_map) {
	#if defined _WIN32
	// Windows should use wide chars by default
	bool default_value = true;
	#else
	// Mac and Linux should not use wide chars by default
	bool default_value = false;
	#endif
	return AsBool(conn_property_map, FlightSqlConnection::USE_WIDE_CHAR)
	.value_or(default_value);
	}

Component(s)

C++, FlightRPC