Allow named_pipe::ServerOptions to set security flags

[dwattttt]

Is your feature request related to a problem? Please describe.
It's not possible to request security access mode permissions for a named pipe created by NamedPipeServer. These correspond to setting the flags WRITE_DAC, WRITE_OWNER, and ACCESS_SYSTEM_SECURITY in the dwOpenMode parameter of the CreateNamedPipeW call (see https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-createnamedpipew ).

This prevents named pipe handles created through tokio from having their security properties set on the pipe via a handle from AsRawHandle.

These flags do not change the IO behaviour of the pipe, and are safe to expose to users.

Describe the solution you'd like
I'd like helpers added to ServerOptions to add these bits to the CreateNamedPipeW call. These would be identical to access_inbound etc, except that they would set WRITE_DAC, WRITE_OWNER, and ACCESS_SYSTEM_SECURITY.

Describe alternatives you've considered
The only alternative would be to produce a handle to the pipe via the native API while additionally requesting these flags. This is not ideal because to open additional server sides to the pipe requires identical flags to be passed for several parameters; without diving into tokio's source it's not possible to know what these are.

Additional context
Allowing security settings to be changed on a named pipe allows users to leverage Windows access control, e.g. to allow or restrict access to the pipe to various users/groups.

[Darksonn]

This feature request sounds good to me.

[dwattttt]

I'm fairly new to github, but https://github.com/dwattttt/tokio/tree/feature/named_pipe_security

[Darksonn]

You will need to open a pull request for your branch to get it merged.