When parsing HTTP request parameters, Rails delegates to a set of parsing
strategies based on the MIME type. If any of these strategies raises an
error Rails rescues it and raises an instance of
`ActionDispatch::Http::Parameters::ParseError` with the same message as
the underlying error.

However, in the presence of malformed JSON, the default parameter parser
for the `application/json` MIME type raises a `JSON:ParserError` with a
message containing the entire malformed JSON string (the request body in
this context). By raising a new error with this same message Rails
inadvertently ends up logging the full HTTP request body at the `fatal`
level. This request body could contain sensitive information or could be
intentionally crafted to be extremely large.

This commit sets the `ActionDispatch::Http::Parameters::ParseError` message
to a static message which mirrors that of the corresponding `debug` log.