[wiz] Add Troubleshooting Note in Readme

[mohitjha-elastic]

Proposed commit message

wiz: add troubleshooting note in README on `event.ingested` requirement for standalone Elastic Agent.

Updated the README to include a troubleshooting note explaining that the `event.ingested` ECS field is
required for transforms in the Wiz integration. This clarification helps prevent transform-related
issues in standalone setups.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

How to test this PR locally

• Clone integrations repo.
• Install elastic package locally.
• Start elastic stack using elastic-package.
• Move to integrations/packages/wiz directory.
• Run the following command to run tests.

elastic-package test -v

Related Issue

• Closes wiz: Add transform requirement for standalone agent #14394

[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

[elastic-vault-github-plugin-prod]

🚀 Benchmarks report

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[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 21d8a18

cc @mohitjha-elastic

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[elastic-vault-github-plugin-prod]

Package wiz - 3.6.0 containing this change is available at https://epr.elastic.co/package/wiz/3.6.0/