`section` metadata field validation

[Mr-Leshiy]

Summary

Implement a corresponding full validation and correct deserialisation of the metadata field section following the specs

• CBOR definition https://input-output-hk.github.io/catalyst-libs/architecture/08_concepts/signed_doc/metadata/#document-type
• Validation https://input-output-hk.github.io/catalyst-libs/architecture/08_concepts/signed_doc/metadata/#section

Description

• Double check the Section type internal implementation (clarify with architects what is the correct format should be, RFC6901 Standard JSON Pointer or what ?)
• Implement a full validation under the SectionRule::check type according to the spec
• Implement a SectionRule constructor, initialising it from the signed_doc.json specs.

[Mr-Leshiy]

Need clarification from architects