feat: use external header file and schema option for admin import example

[fbiville]

No description provided.

[neo4j-connectors]

	Warnings
⚠️	❗ Please include a description of your PR changes.

Pull request should have a description of the underlying changes.

Generated by 🚫 dangerJS against 4ee5a99

[ali-ince]

we should maybe also remove duckdb from dependencies?

[fbiville]

@ali-ince we still use DuckDB in the admin-import example to read the parquet file's columns:

        // 🐤
        private static List<String> readFieldNames(Source source) throws Exception {
            try (var connection = DriverManager.getConnection("jdbc:duckdb:");
                    var statement = connection.prepareStatement("DESCRIBE (SELECT * FROM read_parquet($1))")) {
                statement.setString(1, ((ParquetSource) source).uri());
                var fields = new ArrayList<String>();
                try (var results = statement.executeQuery()) {
                    while (results.next()) {
                        fields.add(results.getString(1));
                    }
                }
                return fields;
            }
        }