Export spreadsheets asynchronously

[alexsegura]

When exporting deliveries on a large range of dates, we are getting 504 timeout errors.

To fix this, the deliveries export needs to be done asynchronously, like when exporting tasks.

[alexsegura]

As an intermediary solution, we could also implement this export using pure SQL, it seems possible with one big query. Because what seems to cause timeouts is the time spent in PHP building objects, not executing SQL.

[alexsegura]

Since 03e689ca610096dd5f23010ead6821463e53c108, the export should be more optimized.

[Paul-Eraman-CoopCycle]

is this still relevant @alexsegura ?