Write, Patch, Read, and Delete data in the Key-Value Store.

The contents of the data map will be stored and returned on read.

Options for writing a KV entry. Set the "cas" value to use a Check-And-Set operation. If not set the write will be allowed. If set to 0 a write will only be allowed if the key doesn’t exist. If the index is non-zero the write will only be allowed if the key’s current version matches the version specified in the cas parameter.