Discussion: Move away from submodules

As a developer I may not want to use submodules when there are other tools available. We briefly discussed this in https://github.com/ISISComputingGroup/IBEX/issues/6131 (and there is some discussion on that ticket) but we ran out of time to make a decision.

## Acceptance Criteria
* Discussion is had about moving away from submodules
* Meeting documented and tickets created

Start by reading issue 6131 and its discussion to understand the unresolved options around moving away from submodules. Arrange the requested discussion, document the meeting, and create follow-up tickets; the acceptance criteria are met when those records exist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.