[Feature] Introduce secondary index for paimon

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/incubator-paimon/issues) and found nothing similar.

### Motivation

Up to now, Paimon use zorder & order sort compaction to speed up query. After sort compaction, files will be sorted by the order of specified columns. But in some situations, for example, we have tens of columns that should be added in the filter column, sometimes all of them come up together, sometimes, just a few of them. Zorder or order compaction can't handle this situation, because too many columns will reduce the effect of sorting. So if the column base number of these columns is small, we can use bloomfilter or other indexes to speed up queries. That's why this PIP comes up. I want to introduce a index framework to support paimon with flexible index system. 

### Solution

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [X] I'm willing to submit a PR!

The issue proposes a flexible secondary-index framework for Paimon, motivated by limitations of zorder and order sort compaction. No files, tests, or concrete solution are named; begin by examining those existing compaction approaches and define the index requirements, with completion requiring an agreed implementation design and scope.

Written by the indexing model from the issue text.