enhancement(codecs): allow configurable null handling in Arrow encoder

[benjamin-awd]

Summary

This PR is a follow-up from https://github.com/vectordotdev/vector/pull/24124#discussion_r2505586130, allowing for sinks using the Arrow encoder to mark fields as nullable.

This is useful when working with downstream systems that handle null values through defaults or computed columns.

For example, in Clickhouse MATERIALIZED/DEFAULT columns are often used to provide metadata for an event:

CREATE TABLE app_events (
    event_id UInt64,
    ingested_at DateTime64(9) DEFAULT now64(9),
)

In this case, it isn't desirable to use a Nullable(DateTime64(9)) type in Clickhouse, since it creates an additional UInt8 column that is never used. This change gives flexibility to users who may not necessarily want the overhead of schema management.

In general, this also makes schema evolution much easier since we won't need to worry about potential breakage during transitions. Dealing with highly nested data also becomes easier, since we won't need to define all possible nulls within a data structure.

Vector configuration

N/A

How did you test this PR?

Unit tests

Change Type

• [ ] Bug fix
• [x] New feature
• [ ] Non-functional (chore, refactoring, docs)
• [ ] Performance

Is this a breaking change?

• [ ] Yes
• [x] No

Does this PR include user facing changes?

• [x] Yes. Please add a changelog fragment based on our guidelines.
• [ ] No. A maintainer will apply the no-changelog label to this PR.

References

Notes

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