Incorrect retrieval of partitions in get_indexes method

[hovaesco]

The current implementation of get_indexes retrieves the column names of the $partitions table instead of providing the actual values/keys of the partitions.

It should query the "table_name$partitions" directly and return the partition column names along with all partition values.

[hovaesco]

https://trinodb.slack.com/archives/CFPVDCDHV/p1721635411307939