chore(PLT-3524): remove SonarCloud setup

[tf-seti]

Jira link: https://typeform.atlassian.net/browse/PLT-3524

SonarCloud is being decommissioned as our unit-test coverage tool.
See the "Measure Unit Test Coverage" Notion page for context.

This PR removes:

• sonar-project.properties (and .sonarcloud.properties if present)
• The sonar-cloud-scan job and its coverage-artifact upload step in .github/workflows/*
• Any SonarCloud/SonarQube badges in README.md

Follow-ups (handled separately by admins):

• Removing the SONAR_CLOUD_TOKEN repo secret
• Archiving the project in SonarCloud

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Created by Sourcegraph batch change jhuliano.moreno/remove-sonarcloud.

[pr-auditor]

✅ Security Analysis Results

Great news! No security issues found in this pull request.

Analysis Summary:

• 📁 Files reviewed: 2
• ✅ No security vulnerabilities detected

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[gitstream-cm]

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[glean-github-app-oauth]

From Glean Code Writer

Updated the PR to remove the remaining SonarCloud reference (the comment # used in SonarCloud scan in the workflow file).

The PR now completely removes all SonarCloud code references:

• ✅ Deleted sonar-project.properties
• ✅ Removed the SonarCloud Scan step from .github/workflows/pull-request.yml
• ✅ Removed the SonarCloud comment from the Node version matrix

Next steps (admin follow-ups):

• Remove the SONAR_CLOUD_TOKEN repository secret
• Archive the project in SonarCloud

[typeform-ops-gha]

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