feat(docs): Introduce conditions metadata field and Conditions document type:

- Added a new `conditions` metadata field to parameter documents and user-submitted documents, specifying required terms and conditions.
- Created a new Conditions document type to define terms users must accept before submitting documents, including validation rules and business logic for acceptance.
- Updated the `signed_doc.json` specification to include the new Conditions document type and its associated metadata.
- Enhanced documentation to clarify the role of conditions in the document submission process and validation requirements.

Author: nathanbogale

docs/src/architecture/08_concepts/signed_doc/docs/.pages

@@ -7,6 +7,7 @@ nav:
   - Category Parameters: category_parameters.md
   - Category Parameters Form Template: category_parameters_form_template.md
   - Comment Moderation Action: comment_moderation_action.md
+  - Conditions: conditions.md
   - Contest Ballot: contest_ballot.md
   - Contest Ballot Checkpoint: contest_ballot_checkpoint.md
   - Contest Delegation: contest_delegation.md