Add support for registry Path

[denis-tingaikin]

Overview

Previously we added a support OPA for registry service. (See at #269)

The second step is to add for registries the possibility to use a zero trust.

For this reason, we planned to add a Path structure for registries.

Link to the Google Docs document

networkservicemesh/api#147 (comment)

References

#269

Solutions

1. Spec: Store spiffeID of NSE in NetworkSerivceEndpoint message api#148
2. Your options

[denis-tingaikin]

@NikitaSkrynnik

For a first step, we could try to implement metadata sending/receiving for the registry service.

Basically, we need to support these cases:

1. client adds its token to the path from metadata
2. server adds its token to the path in metadata
3. server sends a path to the second registry server via metadata