[Proposal] Support Unix domain socket

[daixiang0]

In what area(s)?

/area runtime

/area operator

/area placement

/area docs

/area test-and-release

Describe the proposal

Now Dapr can work well with Service Mesh, while once use Service Mesh, one extra jump cannot be avoided.

If Dapr supports Unix domain socket to passthrough to Service Mesh, there would be a great acceleration, as result in https://stackoverflow.com/questions/14973942/tcp-loopback-connection-vs-unix-domain-socket-performance said.

Also, if Dapr listens to Unix domain socket, APP can passthrough to it then make acceleration too.

[yaron2]

I agree, we recently looked into this. If you can create a POC and post your findings here that would be awesome.

[artursouza]

This seems to be a duplicate of #2864