SOLR-17924: Introduce Configset create and import flows

[malliaridis]

https://issues.apache.org/jira/browse/SOLR-17924

Description

Configsets are one of the core resources of Solr. Creating and importing these are actions that a user may perform, but are not very obvious in our current UI.

Solution

This PR introduces the creation and import flow of configsets.

Tests

Please describe the tests you've developed or run to confirm this patch implements the feature or solves the problem.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended, not available for branches on forks living under an organisation)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide
• I have added a changelog entry for my change

Additional Tasks

• Move to separate PR the dependency updates and migration to new libraries
• Add tests for the new flows / components
• Add documentation of interfaces / components
• Add simple validation rules before creating a new configset (e.g. check for name conflicts with existing configsets)