s3: add Enabled

s3: add [objects]s3-insecure

Disables TLS. Useful for local development.

s3: add NewClient and URL

Centralizes the logic to create an S3 client and get the base URL.

s3: Import middleware from pages.sr.ht

Closes: https://todo.sr.ht/~sircmpwn/pages.sr.ht/19