Build PXF release packages with oldest supported cloudberry

Users cannot use fresh cloudberry-pxf builds with their older cloudberry builds[1]. e.g. pxf-2.1 is not compatible with cloudberry 2.0:

```
PostgreSQL 14.4 (Apache Cloudberry 2.0.0-incubating build 1) on x86_64-pc-linux-gnu, compiled by gcc (GCC) 11.5.0 20240719 (Red Hat 11.5.0-5.0.1), 64-bit compiled on Aug 2
8 2025 15:25:48
(1 row)

gpafiniti=# create extension pxf;
ERROR: incompatible library "/usr/local/cloudberry-pxf-2.1.0/gpextable/pxf.so": version mismatch (dfmgr.c:371)
DETAIL: Server is version Cloudberry 2, library is version Cloudberry 2.1.
```

It seems that Cloudberry version is captured during compilation and aaserted in runtime.

[1] https://github.com/apache/cloudberry/issues/1805#issuecomment-4622858324

Start by reading the Cloudberry issue and comment linked as [1], then trace how fresh cloudberry-pxf release packages capture the Cloudberry version during compilation. Reproduce the reported PXF 2.1 versus Cloudberry 2.0 mismatch and verify that packages built with the oldest supported Cloudberry work with older supported builds.

Written by the indexing model from the issue text.