Fix uploads of large crates to S3 breaking the client

[Mark-Simulacrum]

Currently, we reuse the client for all files that are uploaded per call
to the relevant code. Unfortunately, S3 will prevent connections from
being long-lived (it's unknown what the exact timeout is, but we hit it
relatively rarely). This code attempts to retry S3 uploads up to 3 times
while replacing the client each time.

r? @QuietMisdreavus

[Mark-Simulacrum]

I ran update queue set attempt = 100 where name = 'alt-stm32f30x-hal'; on the DB to temporarily stop building that crate, as we had been attempting to do so for the last 7-10 hours I believe and failing on the upload each time. We'll want to undo that with update queue set attempt = 0 where name = 'alt-stm32f30x-hal'; after deploying this.

[QuietMisdreavus]

Looks good, thanks!