Added counted_keyword type

[JonasKunz]

What does this PR do?

Adds counted_keyword as supported field type in data streams.

Checklist

• [x] ~I have added test packages to test/packages that prove my change is effective.~ I updated an existing test package instead
• [x] I have added an entry in spec/changelog.yml.

Related issues

Part of #698

[elasticmachine]

:green_heart: Build Succeeded

• Buildkite Build
• Commit: 4fbb57a0ec2b052dd59ec605b67411fb4af5da8a

History

• :broken_heart: Build #529 failed 012fe21973312d2b61796748a30a98340362b599
• :green_heart: Build #527 succeeded 71df920608a4d17a3ef3129c3705e3394a11d667