GraphQL ADR: Add analysis of Apollo Server, Client

Document the result of trying Apollo Server out locally, once. Document
everything in the ADR, alongside every relevant link reference in this
focused Apollo context.

Signed-off-by: Marco Miller <marco.miller@ericsson.com>

doc/adr/0002-GraphQL.md

@@ -1,6 +1,6 @@
 # 2. GraphQL
 
-Date: 2022-01-27
+Date: 2022-02-02
 
 ## Status
 
@@ -238,6 +238,25 @@ graph TD
 1. Scaling (only if needed) depending on trace-server scaling accordingly.
 1. Without scaling, deploying GraphQL Server using containers may still help.
 
+#### Apollo Server trial
+
+1. Apollo's [Getting-started][svr-start] steps were tried once, locally, while preparing this ADR.
+1. Those steps simply show how a GraphQL query may request data based on a schema (`index.js`).
+1. For server to know how to provide that data, a `resolver` function was part of `index.js`, then.
+1. [Apollo][svr-start] is [OSS][svr-open], with [***optional*** commercial add-ons][svr-opt].
+   * It is [a TypeScript server based on Node.js][svr-open].
+   * It has [built-in][svr-rest], [REST](#GraphQL-for-TSP-API-(over-REST)) resolver data support.
+   * Should that support not fit TSP's endpoints, [tsp-typescript-client][client-ts] could be used.
+1. Server doesn't require Kubernetes or a container-based deployment, which then remains optional.
+1. Server doesn't require using the [potentially licensed Apollo Studio][svr-opt] either.
+
+#### Apollo Client: optional
+
+* [Apollo Client][svr-client] seems to be mainly [open-source][svr-client-open] too.
+* It is mostly intended as [a caching aid][svr-client-caching]; to be referred to, maybe, later on.
+* It is [based on React][svr-client], but [other integrations are listed][svr-client-open].
+* This ADR doesn't require a deeper analysis yet, given TSP's current clients to integrate first.
+
 #### Testability
 
 [Testing a GraphQL Server using Jest][jest]?
@@ -327,6 +346,13 @@ Each number referring to an aforementioned (previously numbered) risk.
 [py]: https://graphql.org/code/#python
 [relay]: https://www.apollographql.com/blog/graphql/pagination/understanding-pagination-rest-graphql-and-relay/
 [rh]: https://www.redhat.com/en/topics/api/what-is-graphql#pros-and-cons
+[svr-client]: https://www.apollographql.com/docs/react/
+[svr-client-caching]: https://www.apollographql.com/docs/react/caching/overview/
+[svr-client-open]: https://github.com/apollographql/apollo-client
+[svr-open]: https://github.com/apollographql/apollo-server
+[svr-opt]: https://www.apollographql.com/pricing/
+[svr-rest]: https://www.apollographql.com/docs/apollo-server/data/data-sources/#restdatasource-reference
+[svr-start]: https://www.apollographql.com/docs/apollo-server/getting-started/
 [tsp]: https://github.com/theia-ide/trace-server-protocol
 [var]: https://medium.com/the-graphqlhub/graphql-tour-variables-58c6abd10f56
 [vers]: https://graphql.org/learn/best-practices/#versioning