Consolidate edge-internal and edx-internal and possibly sandbox-internal

[robrap]

Context

We learned that the main reason for separate repos were to allow different levels of access to each. This was when these repos contained secrets, that have since been encrypted. This opens the possibility of consolidating.

Additionally, the separate repositories some makes it harder to implement, or remember to implement, similar changes across all environments.

Lastly, containerization will likely change how much code in these repos remains relevant, and would still need to be consolidated.

Acceptance Criteria

• Consolidate edge-internal into edx-internal
• Consolidate sandbox-internal into edx-internal (or decide against)

Additional Notes

• Since the work will change post edxapp containerization, and is likely a lower priority, we shouldn't review this until edxapp containerization is complete. (Possibly other containerization as well.)
• It is unclear how much work is involved for sandbox-internal, and its benefit, so there should be some discovery on that front.
• It may make sense to consolidate (and possibly ticket) parts of the repo at time.