iceberg e2e tests

[DAlperin]

Adds several new tesdrive actions and uses them to write some roundtrip tests.

$ duckdb-execute name=...

Executes SQL statements against a named DuckDB connection. Each line in the command body is executed as a separate statement. The output is not validated, but an error will cause the test to fail.

$ duckdb-execute name=duckdb
CREATE TABLE test_table (id INTEGER, name VARCHAR);
INSERT INTO test_table VALUES (1, 'Alice'), (2, 'Bob');

$ duckdb-query name=... [sort-rows=true]

Executes a query against a named DuckDB connection and verifies the output. The first line of the command body is the SQL query. The remaining lines are the expected output, with columns separated by spaces.

$ duckdb-query name=duckdb
SELECT * FROM test_table
1 Alice
2 Bob

If sort-rows=true is specified, both the expected and actual rows are sorted before comparison. This is useful for queries that may return rows in a non-deterministic order:

$ duckdb-query name=duckdb sort-rows=true
SELECT * FROM test_table ORDER BY id
1 Alice
2 Bob

NULL values are displayed as <null>:

$ duckdb-query name=duckdb
SELECT NULL
<null>

Tips for reviewer

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[def-]

Please document the new $ duckdb-execute/query commands in doc/developer/testdrive.md