[cmd/opampsupervisor]: Add config validation

[BinaryFissionGames]

Description:

• Refactor config to remove some pointers (using a "default config" + override pattern lets us do this, which simplifies some code)
• Validate the config after loading it, and after getting a new config from the opamp server

Link to tracking Issue: Closes #32843

Testing:

• Unit tests for config validation