[FLINK] Switch gluten-flink entrypoint to velox4j FLINK preset

### Description

gluten-flink initializes velox4j via `Velox4j.initialize()` in `TaskManagerRunner`. velox4j historically only shipped a `SPARK` preset, so gluten-flink inherited Spark function semantics.

velox4j now adds a sibling `FLINK` preset (bigo-sg/velox4j#54), backed by `velox/functions/flinksql/`. The default remains `SPARK`, so gluten-flink must explicitly opt in via `Velox4j.configure(Preset.KEY, Preset.FLINK)` before `Velox4j.initialize()`.

### Gluten version

main branch

Start by reading the gluten-flink entrypoint in TaskManagerRunner and trace the existing Velox4j initialization. Done means the FLINK preset is explicitly configured before initialization, with the gluten-flink tests or build passing.

Written by the indexing model from the issue text.