[Stack Monitoring] Add compatibility with 9.x

[consulthys]

Proposed commit message

Add constraint for 9.0.0 for Stack Monitoring integrations

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

cc @jamiehynds

[elastic-vault-github-plugin-prod]

🚀 Benchmarks report

To see the full report comment with /test benchmark fullreport

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 4952bb4

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
57.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[elastic-vault-github-plugin-prod]

Package beat - 1.0.1 containing this change is available at https://epr.elastic.co/package/beat/1.0.1/

[elastic-vault-github-plugin-prod]

Package elasticsearch - 1.18.0 containing this change is available at https://epr.elastic.co/package/elasticsearch/1.18.0/

[elastic-vault-github-plugin-prod]

Package kibana - 2.7.0 containing this change is available at https://epr.elastic.co/package/kibana/2.7.0/