content_export_* modules should document that chunk_size_gb doesn't work with syncable format

[jeremylenz]

SUMMARY

If you pass format=syncable, the chunk_size_gb param is ignored. Syncable format exports don't support chunking. But this isn't mentioned anywhere in the documentation.

ISSUE TYPE

• Bug Report

EXPECTED RESULTS

If I can't get a chunked syncable export, either an error informing me of this, or API docs that clearly state it before I try my export

ACTUAL RESULTS

a non-chunked syncable export