codeintel: Make log contents structured (Step 2: GraphQL)
Created by: efritz
Related to https://github.com/sourcegraph/sourcegraph/issues/15941.
This PR updates the GraphQL resolvers available around LSIF indexes (auto-indexing records). The new schema is "inverted" in that we don't have a split between configured steps and execution trace, but instead have a list of "steps" which consists of the configuration data as before and, if executed, will contain additional data about the command that actually runs in the executor.