Fix Inconsistent key encoding for bootstrapping column stats in 0.x

[vamsikarnika]

Bug Description

What happened:
When column stats is enabled on 0.x branches which already contains files partitions, during bootstrapping key encoding considers entire partition path while readers only consider partition value alone.

This doesn't impact data consistency/correctness, but can affect the column stats pruning effectiveness

What you expected:

Steps to reproduce:

1. Create a Hudi table with metadata table enabled, but column stats disabled
2. After a commit, enable column stats
3. column stats key encoding differs from expected key using partition value.

Environment

Hudi version: 0.14, 0.15
Query engine: (Spark/Flink/Trino etc)
Relevant configs:

Logs and Stack Trace

No response