Fix outdated documentation in Scalability reference page

[ShinjoWang]

Summary

There are two documentation issues on the Scalability reference page.

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1. Reference to removed throttle-limit / throttleLimit

The following sentences reference throttle-limit (XML) and throttleLimit (Java), both of which were removed in Spring Batch 6:

Java config section:

Similar to the multi-threaded step's throttleLimit method, the gridSize method prevents the task executor from being saturated with requests from a single step.

XML config section:

Similar to the multi-threaded step's throttle-limit attribute, the grid-size attribute prevents the task executor from being saturated with requests from a single step.

Since both throttleLimit and throttle-limit no longer exist in Spring Batch 6, these comparisons are misleading and should be updated. A suggested replacement for both:

The gridSize method (or grid-size attribute) prevents the task executor from being saturated with requests from a single step.

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2. Broken link and outdated reference to partition job sample

The following sentence contains a broken link and references XML-based configuration that no longer exists:

The unit test suite for Spring Batch Samples (see partition*Job.xml configuration) has a simple example that you can copy and extend.

The linked path (https://github.com/spring-projects/spring-batch/tree/main/spring-batch-samples/src/main/resources/jobs) no longer contains partition job XML files.

Also, the placement is inconsistent with other sections — Local Chunking and Remote Step both place the sample link at the end of their respective sections, whereas this reference currently sits in the middle of the Partitioning section, before the PartitionHandler, Partitioner, and Binding Input Data to Steps subsections.

Would it make sense to remove the sentence from its current location and add the following at the end of the Binding Input Data to Steps subsection, consistent with the pattern used in other sections?

You can find a complete example in the Partitioning Sample

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Affected file

spring-batch-docs/modules/ROOT/pages/scalability.adoc

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I'd be happy to submit a pull request for this if the proposed direction looks good to you.