[FEATURE REQUEST] Dynamic saltenvs for s3fs mounts? (__env__)

[mdschmitt]

Is your feature request related to a problem? Please describe.
As it stands, there are only 2 s3fs mount options:

1. A single bucket per environment

s3.buckets:
  production:
    - bucket1
  staging:
    - bucket2

2. Multiple environments per bucket

s3.buckets:
  - bucket1
  - bucket2

However, option 2 mandates that the bucket contents comply with a s3://bucket/<saltenv>/xxx file structure.

Describe the solution you'd like
It'd be quite useful to simply specify __env__ in option 1 and have the best of both worlds (any bucket file structure, applied to any named saltenv). Like so:

s3.buckets:
  __env__:
    - bucket1

Describe alternatives you've considered
N/A

Additional context
Example: an S3 bucket containing build artifacts from a CI system. Binaries/jars/rpms/debs aren't necessarily saltenv-specific, so creating dedicated s3://<environment>/builds directories doesn't make much sense (and the CI doesn't/shouldn't need to know anything about saltenvs).

...but if I just put the bins at the root of the bucket, I need to restart the saltmaster with new s3.buckets syntax every time I want to use a different saltenv (which, for me, is often just a temporary WIP git branch)..