Make chunk uploads the default for Proguard files

[szokeasaurusrex]

Chunk uploads are available for Proguard files, but they are not the default and have been labelled as experimental. Before we can make them the default, we must do the following:

• Check whether the server supports Proguard chunked uploads, and only use chunk uploading if yes
• We also plan to remove support for release association along with this change, so we don't need to wait for assembly to complete when uploading. This means that making chunk uploading the default will be a breaking change, so we will need to make this change in a major release