adding large attachments with the SOAP api causes OOMEs

Using the SOAP API to add attachments to issues can cause JIRA to throw an OutOfMemoryError. This can cause JIRA to become unresponsive and could be used in a denial of service attack, which is especially bad in a multi tenant world.

This happens when using the addAttachmentsToIssue (now deprecated) with small files (~1MB), and also when using addBase64EncodedAttachmentsToIssue with large files (~100MB).

The SOAP API implementation should detect attachments that are larger than a certain size and reject the request if the size is exceeded.