do not coerce request body property values

[cdimascio]

This PR remove type coercion from request bodies.
This should fix the following issues:

• Request body property is coerced e.g. ("123" coerced to123) Request body property is coerced e.g. ("123" coerced to123) #249
• Any work-around for ajv's undesired number coercing rules? Any work-around for ajv's undesired number coercing rules? #268.
  Note: This fix will ensure that nulls passed as numbers (by default) fail validation.
  Issue Any work-around for ajv's undesired number coercing rules? #268 would like support for round-trip NaNs which this does not solve
• coerceTypes is all or nothing coerceTypes is all or nothing #243

[MadMango]

I just found this issue after upgrading the library and finding that it's broken because I'm sending numbers as strings to our APIs.

There are good reasons to have coercion enabled as explained here

@cdimascio What was the rationale behind removing the option completely? The problem you references could have been solved by just setting coerceTypes to false.

[cdimascio]

Thanks for your input. Here is the rationale. Happy to open the discussion.
#396 (comment)