docs(task-testing): add for Web Modeler

[philippfromme]

Related to https://github.com/camunda/product-hub/issues/2660

Description

Re-adds task testing docs for Web Modeler after task testing was merged.

8.8 Docs Web Modeler section

8.9 Docs Web Modeler Section

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the Documentation team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• The commit history of this PR is cleaned up, using {type}(scope): {description} commit message(s)

• My changes are for an upcoming minor release and are in the /docs directory (version 8.9).
• My changes are for an already released minor and are in a /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[github-actions]

👋 🤖 🤔 Hello, @giorgionaps! Did you make your changes in all the right places?

These files were changed only in docs/. You might want to duplicate these changes in versioned_docs/version-8.8/.

• docs/components/modeler/web-modeler/validation/task-testing.md

These files were changed only in versioned_docs/version-8.8/. You might want to duplicate these changes in docs/.

• versioned_docs/version-8.8/components/modeler/web-modeler/task-testing.md

You may have done this intentionally, but we wanted to point it out in case you didn't. You can read more about the versioning within our docs in our documentation guidelines.

[Copilot]

Pull request overview

This PR reintroduces and wires up task testing documentation for Web Modeler in both the current (8.9) docs and the 8.8 versioned docs, aligning with the recent product rollout of task testing.

Changes:

• Added Web Modeler task testing guides (new pages) for both 8.8 (versioned_docs) and current docs (docs) including feature overview, usage instructions, and result interpretation.
• Updated sidebars and cross-links so Web Modeler task testing appears in navigation and is referenced from existing task testing and Desktop Modeler docs.
• Added task testing success screenshot assets and linked them from the new documentation pages.

Reviewed changes

Copilot reviewed 8 out of 14 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
versioned_sidebars/version-8.8-sidebars.json	Adds Web Modeler task testing page to the 8.8 sidebar under the Web Modeler section.
versioned_docs/version-8.8/components/modeler/web-modeler/task-testing.md	New 8.8 Web Modeler task testing guide describing when and how to run task tests and interpret the results.
versioned_docs/version-8.8/components/modeler/web-modeler/img/task-testing/task-testing-success.png	New 8.8 screenshot asset used in the Web Modeler task testing guide.
versioned_docs/version-8.8/components/modeler/task-testing.md	Updates general task testing overview to link to the new 8.8 Web Modeler task testing guide.
versioned_docs/version-8.8/components/modeler/desktop-modeler/task-testing.md	Adds cross-links from Desktop Modeler task testing docs to Web Modeler and related concepts/variables docs for 8.8.
sidebars.js	Adds the Web Modeler task testing validation page to the main (8.9) sidebar under the Web Modeler validation section.
docs/components/modeler/web-modeler/validation/task-testing.md	New current Web Modeler task testing guide (8.9), mirroring the 8.8 content but under the validation section.
docs/components/modeler/web-modeler/img/task-testing/task-testing-success.png	New current-docs screenshot for successful task test execution.
docs/components/modeler/task-testing.md	Updates general task testing overview to link to the new Web Modeler validation task testing page.
docs/components/modeler/desktop-modeler/task-testing.md	Adds Web Modeler and variables links to the current Desktop Modeler task testing docs.

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[giorgionaps]

Minor edits committed directly to the branch. LGTM!