Define the multipleOfPrecision option for ajv to handle javascript number precision

[DyspC]

Summary

Prism had trouble with the OAI multipleOf number constraint because the default ajv validation does not behave properly with non integer multipliers cf. https://github.com/ajv-validator/ajv/blob/master/lib/vocabularies/validation/multipleOf.ts

Eg: -4.02 multipleOf 0.01 was rejected because JS says -4.02 / 0.01 = -401.99999999999994

This PR adds the AJV option to handle an error margin (1/1000th at the moment)

Checklist

• The basics
  • I tested these changes manually in my local or dev environment
• Tests
  • Added or updated
  • N/A
• Event Tracking
  • I added event tracking and followed the event tracking guidelines
  • N/A
• Error Reporting
  • I reported errors and followed the error reporting guidelines
  • N/A

Context

ajv-validator/ajv#84
ajv-validator/ajv#652

[chohmann]

@DyspC can you add a few test cases to cover this functionality?

[chohmann]

@DyspC we really appreciate the PR! Since we haven't heard from you about adding tests to this, we're going to close the PR. Feel free to re-open with some tests if you get the time in the future!