CDK and doc: use "additionalProperties": true instead of false

[alafanechere]

A SAT addition (#14878) enforces connectors to use the value true for the additionalProperties field that can be declared in json schema of spec or stream.
Our tutorials and code generation template are not up to date to follow this new rule.

Acceptance criteria:

• All occurrences of "additionalProperties": false are replaced to "additionalProperties": true in tutorial and template files. Grepping in *.md and *.hbs should be enough.
• If the schema generator tool (tools/schema_generator) should not generates schema with "additionalProperties": false please make it generate "additionalProperties": true