Doc: Update doc to display the results of the table partitions query

[lvyanquan]

In the pr of #4516, we added specId for partitions metadata table, but the document of query(https://iceberg.apache.org/docs/latest/spark-queries/#partitions ) hasn't been changed to adapt to that.
What's more, the ResultSet structures are not the same between partitioned and not-partitioned tables.

query example:

0: jdbc:hive2://host:10000> create table p (id int, age int) using iceberg partitioned by (id);
0: jdbc:hive2://host:10000> create table np (id int, age int) using iceberg;
0: jdbc:hive2://host:10000> insert into p(id, age) values (1,1),(2,2),(3,3);
0: jdbc:hive2://host:10000> insert into np(id, age) values (1,1),(2,2),(3,3);
0: jdbc:hive2://host:10000> select * from spark_catalog.kunni_db.p.partitions;
+------------+---------------+-------------+----------+
| partition  | record_count  | file_count  | spec_id  |
+------------+---------------+-------------+----------+
| {"id":2}   | 1             | 1           | 0        |
| {"id":3}   | 1             | 1           | 0        |
| {"id":1}   | 1             | 1           | 0        |
+------------+---------------+-------------+----------+
3 rows selected (0.185 seconds)
0: jdbc:hive2://host:10000> select * from spark_catalog.kunni_db.np.partitions;
+---------------+-------------+
| record_count  | file_count  |
+---------------+-------------+
| 3             | 3           |
+---------------+-------------+
1 row selected (0.126 seconds)

[szehon-ho]

I think the docs make sense overall, one comment.

[szehon-ho]

Im not sure about adding non-partitioned example for "partitions" table , as I think its something few users would need, but it is right under the header so most people have to scroll past to see what they really want to see (the schema). Id suggest removing it for now, which would be consistent with the other tables, if it sounds reasonable to you?

[lvyanquan]

Yeah, I I keep the result of partitioned table and display the result of non-partitioned table using note to make it more understandable.

[lvyanquan]

addressed it.

[szehon-ho]

OK its fine with me, left one small nit

[szehon-ho]

I just realized "this table... it" will be wrong because we mean different tables (data table and metadata table)

How about this fix?

"For unpartitioned tables, the partitions table will contain only the record_count and file_count columns."

[lvyanquan]

Thanks, addressed it.

[szehon-ho]

Sorry I re-read this and just one small thing to address, then I think we can merge it.

[szehon-ho]

Merged, thanks @lvyanquan