Configure upload size and execution time

Summary:
As a media site, we want to allow large uploads.

Pixelfed recommends 64M, but as the base image has already a memory limit
set at 128M, this limit can be reused to simplify the configuration reading.

Some tasks can be a little long, so we allow larger execution time.

Ref T1481

Test Plan: Tested on Equatower with > 2M upload

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1481

Differential Revision: https://devcentral.nasqueron.org/D2029