Website: Clean up and restructure documentation folders

[morri-son]

Description:
Create a new documentation structure on the website.

Scope:

• Add a Concepts section
• Move content from the Important Terms document to a new concept document (like ocm_components.md)
• Include a link to the OCM specification repository in the new OCM Components concept document.
• Create placeholder documents for future concepts as target for any links from other docs (e.g., SBoD vs SBOM, input and access types, component constructor, etc.)
• Delete the Important Terms document
• Delete the Specifications document

Definition of Done

• Concepts section is created
• Content from "Important Terms" moved to new "OCM Components" document
• Link to OCM specification included in new "OCM Components" document
• Placeholder documents for future concepts created
• "Important Terms" document deleted
• "Specifications" document deleted

[AlexandraHaenig]

will be finalised in the next sprint.