Allow streams to be created with a first offset other than 0

[kjnilsson]

Is your feature request related to a problem? Please describe.

This could be useful when needing to re-create a stream (for some reason) but still align to externally stored consume offsets.

https://groups.google.com/g/rabbitmq-users/c/GApahOXZOUU

Describe the solution you'd like

There is already code in osiris_log to specify an initial_offset. This is currently only used by new replicas but could be extended to be supported by the writer role also.

Describe alternatives you've considered

No response

Additional context

No response