Add Patrol docs to testing section

[pdenert]

Description of what this PR is changing or adding, and why:
Add info about Patrol E2E testing framework to:

• Testing - Overview
• Integration testing - Introduction
• Test a plugin
• new page: Write and run a Patrol test

Issues fixed by this PR (if any):
#13128

PRs or commits this PR depends on (if any):

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks
  of 80 characters or fewer.

[gemini-code-assist]

Code Review

This pull request introduces documentation for the Patrol testing framework as an alternative to the standard integration_test package for Flutter. The changes include a new comprehensive guide on writing and running Patrol tests, updates to the testing overview and plugin testing pages to highlight Patrol's native UI interaction capabilities, and the addition of Patrol-related CI/CD resources. The review feedback focuses on adhering to the repository's style guidelines regarding semantic line breaks (80-character limit) and the proper use of backticks for commands and flags.