Replace lambda validation with API Gateway request validation

[ashley-evans]

Value Added

Reduces lambda runtime costs. Reduces the responsibilities of the current lambda's that invoked by API Gateway

Description

Currently all of the existing lambdas perform validation on the request event/records using the middy validation middleware. This should be replaced by JSON validation on the API Gateway itself.

Acceptance Criteria

AC01

• Replace validation performed during lambda functions that are invoked by API gateway with equivalent API Gateway request validation

AC02

• Add automated testing to ensure that the same validation is performed against the request model as previously with the lambda

AC03

• All changes required to achieve AC01/02 must be carried out via SAM/Cloud formation template updates