Entity groups content pack support for streams

[ryan-carroll-graylog]

Adds content pack support for entity groups and handling in streams.

Description

Implements creation, export/import, and installation of content packs with entity groups as part of streams.

Motivation and Context

Closes: https://github.com/Graylog2/graylog-plugin-enterprise/issues/7420

How Has This Been Tested?

Locally in dev environment.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.