Introducing core package in the data-prepper-core module

[san81]

Description

PR looks huge but there is no real code change. It is only a package restructuring.

Organizing core data prepper code base into a package named core so that we can minimize the spring component scanning to the required packages and avoids rescanning of the same packages when we initiate plugin specific isolated spring context initialization. The following modules are modified to in order and their corresponding spring context scanning package names modified

• org.opensearch.dataprepper pacakge under data-prepper-core module is now moved to org.opensearch.dataprepper.core
• Under data-prepper-main module introduced core package but only moved two classes related to DataPrepper Argument classes
• Under data-prepper-pipeline module classes under org.opensearch.dataprepper.validation package to org.opensearch.dataprepper.core.validation package.
• All the corresponding Test classes are also moved relative to their original class file
• Rest of the changes are just to fix the import statements in other classes where the refactored classes are references.

Issues Resolved

• Avoids double scanning of the class files while initializing plugin specific isolated spring DI context
• Enables to ingest any Plugin configuration as a bean

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[dlvenable]

Thank you @san81 for this very help contribution. This is a good clean-up to the project.

I have a couple comments about some classes that perhaps should not be moved. Other than that, this looks good to me.