L108: Node.js Reflection Server Library

[jtimmons]

adding proposal as discussed in grpc/grpc-node#79

[linux-foundation-easycla]

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• ✅ login: jtimmons / name: Justin Timmons (040c8de, b0d30cb, 258ad37, 267c436, 5547e71, 6e88447, b02b5e0)

[murgatroid99]

I took the liberty of updating the PR title. The proposal itself is for the "Node.js Reflection Server Library", and the status can be managed within the text of the proposal document. Please list me as the approver, create a discussion thread as described in the README's process section, and update the status in the document to "In Review".

In addition, L107 is already reserved for #395, so please update the PR title and text to L108.

[murgatroid99]

As we discussed in grpc/grpc-node#79, it should be possible for the Server class to expose all of the necessary information to support reflection. The reflection library should have an API to take advantage of that by making it as simple as possible to add reflection, e.g. it could export a top-level function enableReflection(server). This is also important because a server can have services based on proto files that the user does not have direct access to: in grpc-js, the addAdminServicesToServer adds the channelz service, and also the CSDS service if using xDS.