Add `s3_prefix` env var for `curl-api-upload-file`
Add `s3_prefix` env var for `curl-api-upload-file`

- adds a prefix (separated with `.`) to all uploaded files

E.g.:

```sh
$ curl-api-upload-file ~/sample-photos/pool/<1-10>.png
 # uploads 1.png to `{{uuid}}.1.png`
 # uploads 2.png to `{{uuid}}.2.png`
 # ...
$ s3_prefix=benizi curl-api-upload-file ~/sample-photos/pool/<1-10>.png
 # uploads 1.png to `benizi.{{uuid}}.1.png`
 # uploads 2.png to `benizi.{{uuid}}.2.png`
 # ...
```

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