[23150] Docs - Apply custom templates to included IDL files (backport #1066)

[mergify]

Description

This PR updates Fast DDS documentation to exemplify how custom templates can be applied to included IDL files.

@Mergifyio backport 3.1.x 3.0.x 2.14.x 2.10.x

Related implementation PR:

• [23150] Apply user template to included IDL files Fast-DDS-Gen#472

Contributor Checklist

• Commit messages follow the project guidelines.
• Code snippets related to the added documentation have been provided.
• Documentation tests pass locally.
• 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.
• CI passes without warnings or errors.

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This is an automatic backport of pull request #1066 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of bf0dfe6 has failed:

On branch mergify/bp/2.10.x/pr-1066
Your branch is up to date with 'origin/2.10.x'.

You are currently cherry-picking commit bf0dfe6.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   code/FastDDSGenCodeTester.cpp
	both modified:   docs/fastddsgen/dataTypes/dataTypes.rst

no changes added to commit (use "git add" and/or "git commit -a")

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