[CNTR-746] Allow swagger validation against custom schemata

[hornc]

In order to enforce the requirements from CNTR-743, add a method to validate swagger.json against additional (organisational specifc) json schemata.

CNTR-743 requirements:

• All entities defined in the definitions section must include an explicit type: object attribute. This forces the entity to be validated.
• All arrays must be explicitly 'typed', either via $ref to an entity that itself is typed (i.e. has type:object), or via an explicit type: xxx attribute in the items section of the array spec.

[gingermusketeer]

Be good to add a test that ensures this raises an error when the schema is incorrect

[hornc]

Test added, thanks @gingermusketeer !

[gingermusketeer]

LGTM