Update docs to mesh, add header forwarding

Docs update

We publicly renamed Rosetta to Mesh, this release contains all the docs updates for that rename

Header Forwarding

Why

In order to support some common use cases, Mesh servers need the ability to pass request headers through to the native nodes, and to return headers from native node requests back to the caller.

Use cases:

• passing a client ID header to the nodes — this client ID shouldn't originate with the Mesh server since it may have many different callers, so it should be passed through to the native node requests
• sticky session cookies — to support sticky sessions on native nodes, AWS uses cookies. Cookies are managed by the Cookie and Set-Cookie headers, which will need to be passed from the caller to the native node, and returned from the native node ALB to the caller

Solution

The HeaderForwarder type extracts headers from Mesh requests and forwards them to native node requests. It also watches potentially many native node responses and combines those headers to add them to a Mesh response.

To accomplish this, HeaderForwarder offers three different types of injection:

• Server handler middleware — used to capture headers from the Mesh request for outgoing header forwarding, and to add native node response headers to the Mesh response
• http.RoundTripper implementation — used to add outgoing headers to HTTP requests and capture incoming response headers
• grpc.UnaryClientInterceptor implementation — used to add outgoing metadata to gRPC requests and capture incoming response metadata

A few key features:

• opt-in — users of this library can choose to use or not use this feature
• allows forwarding only specific headers
• assigns every request a unique ID, which is used to associate headers from native node responses back to Mesh request/responses

Changelog

Full changelog: v0.8.5...v0.8.7