`uploads` module should function with default config

[NathanFlurry]

Motivation

Users should not be required to connect S3 to run a dev cluster.

Users depends on the uploads module, but it may not be configured.

Implementation

• Throw a runtime error if s3 is not configured for relevant paths.
• Make the s3 path nullable

[linear[bot]]

OGB-56 `uploads` module should function with default config