Server - Implement search filters in content packs

[ryan-carroll-graylog]

Description

Implements the ability to export and import saved search filters via Content Packs. Also handles the dependency resolution for other Content Pack entities that reference saved search filters.

Also see enterprise PR: https://github.com/Graylog2/graylog-plugin-enterprise/pull/7111

/nocl

Motivation and Context

Closes: https://github.com/Graylog2/graylog-plugin-enterprise/issues/6607

How Has This Been Tested?

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.