Add timestamp and biddercode to event URL - refactored

[rpanchyk]

See parent PR #635

[DGarbar]

NumberUtils.isDigits() or StringUtils.isDigits(), (but we still need to check for null bc this value is not required)

[rpanchyk]

Both util methods doesn't guaranteed Long range value checking, so NumberFormatException can be thrown. Don't think they are useful here.

[DGarbar]

suggest

   for (PutObject putObject : putObjects) {

            JsonNode value = putObject.getValue();
            if (biddersAllowingVastUpdate.contains(putObject.getBidder()) && value != null) {
                final String updatedVastXml = modifyVastXml(value.asText(), putObject.getBidid(),
                        putObject.getBidder(), accountId, putObject.getTimestamp());
                value = new TextNode(updatedVastXml);
            }

            updatedPutObjects.add(putObject.toBuilder()
                    // remove "/vtrack" specific fields
                    .bidid(null)
                    .bidder(null)
                    .timestamp(null)
                    
                    .value(value)
                    .build());
        }

[rpanchyk]

kind of taste-)

[DGarbar]

I'd also added .timestamp(1231221L) to test