Investigate file size restriction enforcement for /wiki/rpc/soap-axis/confluenceservice-v1 / addAttachment API

The cause for HOP-314 was the usage of the /wiki/rpc/soap-axis/confluenceservice-v1 / addAttachment API with relatively large files (~82mb). If I recall right, our attachment file size in OnDemand is set to 100mb (CONFDEV-3606), but I've got no idea if it is enforced if using this API and if so it's probably after the deserialisation. The limit wouldn't have mattered anyway in the above mentioned case.

Please investigate if a limit of 100mb is still feasible (imo it's way too high, I would even suggest reducing it to ~10-15mb) as the production max heap size is 512mb. Please also ensure that the limit is enforced when using the above mentioned API before it's getting deserialised since it'll cause a memory footprint of at least double the size.

Maybe we should enforce the setting of the Content-length header via a filter for these requests, and enforce the limit via that (even if it's not accurate). We could also experiment with just setting the maxPostSize on the container.