Not a blocker for this PR, but probably could make our lives easier in the long-run by just attaching a `SPEC_IDENTIFIER` and `GROUP_SPEC_IDENTIFIER` (or similar), which could house everything in the `EcsGroupSpec` interface. Then fewer changes are required if we ever need to pull more data out of the group spec.

[lgestc]

Not a blocker for this PR, but probably could make our lives easier in the long-run by just attaching a SPEC_IDENTIFIER and GROUP_SPEC_IDENTIFIER (or similar), which could house everything in the EcsGroupSpec interface. Then fewer changes are required if we ever need to pull more data out of the group spec.

type SpecInternals = {
  [FIELD_SPEC_IDENTIFIER]?: EcsFieldSpec;
  [GROUP_SPEC_IDENTIFIER]?: EcsGroupSpec;
};

Originally posted by @lukeelmers in #18 (comment)