Guidance implementation for creating Profile Crates and using them for validation

> **Note:**
> This is not yet part of the specification! What we do have already, is support for multiple "conformsTo" values, meaning multiple profiles being specified for a crate. Please remember, both are features of the 1.2-DRAFT specification and there is no guarantee they will make it into the final version.

If you have an urgent need, feel free to discuss further proceeding here. Code contributions are always welcome. What may implement at some point:

- A specific builder pattern for the suggested profile crates
- A specific validator supporting the suggested methods for describing the crate using a profile crate

Resources:

- https://www.researchobject.org/ro-crate/1.2-DRAFT/profiles.html#profile-crate

No files, tests, or entry points are named. Start by reading the linked RO-Crate 1.2-DRAFT profile-crate guidance and then locate the repository's existing crate-building and validation APIs; done would require agreed builder and validator behavior for profile crates, backed by tests.

Written by the indexing model from the issue text.