Support SSE-C key per-operation

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

I'd like to use SSE-C encryption with per-file encryption keys.

**Describe the solution you'd like**

Would be nice to support per-operation SSE-C keys. IIUC right now it is only supported per-store.

**Describe alternatives you've considered**

Make a store per operation but at the cost of a lot of overhead and network connections (?)

**Additional context**

Start by reviewing how SSE-C is currently configured at the store level and how individual operations receive store options. Trace the operation APIs to determine where a per-operation key could be passed, then compare that with the existing store-per-operation workaround. Done means supported operations can use distinct SSE-C keys without requiring a separate store.

Written by the indexing model from the issue text.