#259 - JsonStreamWriterTask: add a mode option

[njoubert-cleverage]

Description

Fixes #259.

JsonStreamWriterTask already exists (since #168, with spl_file_object_flags / json_flags since #172) and already matches most of the issue: blocking task, each array input written as one line with JsonStreamFile::writeLine(), proceed() outputs the file path, {date} / {date_time} / {timestamp} / {unique_token} placeholders, non-array input rejected with an \UnexpectedValueException. Documented in docs/reference/tasks/json_stream_writer_task.md.

What was missing, added here:

• mode option (string, default wb, which was hard-coded): e.g. ab to append to an existing JSON Lines file;
• release of the file on finalize(), as the CSV tasks (CsvWriterTask: a non-array input throws a TypeError when headers is null, and the task cannot run again after finalize() #241).

Tests added in JsonStreamWriterTaskTest: overwrite by default, ab mode appends, mode type validation, placeholders replaced in both the written and output path, non-array input, finalize(). PHPStan, PHPUnit (869 tests), PHP-CS-Fixer and Rector pass. Demonstrated by demo.file.json_stream_writer_append in process-bundle-demo.

Requirements

• Documentation updates
  • Reference
  • Cookbooks
  • Changelog
• Unit tests

Breaking changes

None: new option whose default is the previous behaviour.

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