fix: join on bucket_id column

Summarize the changes

• fix: join on bucket_id column

• For queries that want to join on bucket_id column, we had wrong logic of removing that column from child scan, now if we have bucket_id column in join we won't delete bucket_id from scan node.
• Fix conflict resolution for join on bucket_id: if we see that join is done on bucket_id, we don't need any motions.

Note: there is still a problem when we don't use "bucket_id" in join condition:

select t1."bucket_id", t2."bucket_id" from t1
join t2 on ...

This query will fail with error that it can't find "bucket_id" column.

Ensure that

• New code is covered by unit and integration tests.
• Related issues would be automatically closed with gitlab's closing pattern (Closes #1, #2).
• Public modules are documented (check the rendered version with cargo doc --open).
• (if PEST grammar is changed) EBNF grammar reflects these changes (check the result with railroad diagram generator.

Next steps

• Update sbroad submodule in picodata/picodata.
• (if EBNF grammar is changed) create a follow-up issue in picodata/docs.

Closes #590 (closed)