[Change Proposal] Identify and check additional features that may change between stack versions

[jsoriano]

To be able to use checks based on the package spec versions, we need to be able to model as many features as possible in each package.

Try to identify and check the use of additional features, so we can control what version of the package spec starts including them:

• Ingest processors used in ingest pipelines.
  • Add validation for allowed processors in ingest pipelines #586
• Aggregations used in dashboard queries.
  • Would be to find operationTypes... not sure if very reliable.
• Elasticsearch settings.
  • Stricter validation of data stream settings #587

This may need to be part of package spec v3 as may be breaking for some cases.

[jsoriano]

Closing this by now, though we may add more checks for dashboards in the road to v3.