[SPIKE] Acceptable CODEOWNERS Groups Should Inherit from Parent Group

Proposal

Currently, as per the CODEOWNERS documentation for the CODEOWNERS file to reference a group it is not under you must first add that group to the project.

The documentation describes a situation like this:

group-x
├── subgroup-y
│   └── project-b
└── project-a

In this scenario, for @group-x/subgroup-y to be a valid CODEOWNERS target, that group must be first invited to project-a.

However, given the following layout, where project-a is instead a project that exists under subgroup-z:

group-x
├── subgroup-y
│   └── project-b
└── subgroup-z
    └── project-a

If subgroup-y is invited to subgroup-z, that group membership isn't inherited by project-a and subgroup-y must additionally be invited to project-a.

I would like to propose that groups invited to other groups are inherited by their subprojects as CODEOWNERS.

Real usecase:

group-x
├── engineering-group
├── datascience-group
└── product-group
    ├── project-a
    └── project-b

In this case, both engineering-group and datascience-group contain no projects, and are only used to hold members. Both groups are invited to product-group which contains common projects, but they still have to be added additionally to projects within product-group for CODEOWNERS to recognise @group-x/engineering-group or @group-x/datascience-group as valid targets.