Use `.jsonl` instead of `.json` as the extension for json lines

[Dietr1ch]

The examples did a conversion that threw me off,

• https://github.com/datafusion-contrib/bdt#convert-parquet-to-newline-delimited-json

json is the wrong extension, even if some parsers seem to work fine.

https://jsonlines.org/ explicitly mentions that .jsonl would be preferred.

[Dietr1ch]

This is inherited from datafusion using JSONL, but calling it JSON,

• https://github.com/apache/datafusion/blob/main/datafusion/common/src/file_options/file_type.rs#L30
• datafusion/core/src/datasource/file_format/json.rs

It doesn't help that NDJSON (newline-delimited JSON) forked JSONL¹.

Changes here would be simply adding a new type of output in src/lib.rs

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Footnotes

1. It seems they mostly align today except for NDJSON allowing to eat up your empty lines, which is fair as you can use an empty tuple ({}) to signal "one nothing" and avoid trouble with missing/present new-line at the end of the file. ↩