Fix default history depth in examples

[raulojeda22]

Description

We used to have a default limit in max_samples_per_instance of 400, until this PR changed it to 0 (unlimited): #6261

These examples used that value to set the depth if the param -s was not set (samples), so with default values, just a publisher and a subscriber, the example failed with this error:

2026-08-10 14:18:19.050 [RTPS_QOS_CHECK Error] HISTORY DEPTH must be higher than 0 if HISTORY KIND is KEEP_LAST. -> Function check_qos
2026-08-10 14:18:19.050 [app_name Error] DataWriter initialization failed -> Function main

This PR fixes this issue by adding a constant with a default depth to the examples for when the samples parameter is not set.

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A Any new/modified methods have been properly documented using Doxygen.
• N/A Any new configuration API has an equivalent XML API (with the corresponding XSD extension)
• Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• Changes are API compatible.
• N/A New feature has been added to the versions.md file (if applicable).
• N/A New feature has been documented/Current behavior is correctly described in the documentation.
• N/A Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• If this is a critical bug fix, backports to the critical-only supported branches have been requested.
• Check CI results: changes do not issue any warning.
• Check CI results: failing tests are unrelated with the changes.