Allow systems in a chain to access the name of the outer `ChainSystem`

## What problem does this solve or what need does it fill?

When chaining systems together (especially generic systems), it would be useful to get more detailed debug information about which other systems it is currently being chained with.

## What solution would you like?

Some sort of extension to the `SystemName` param from #5731. Ideally, there would be a method `outer_system_name`, which returns the name of the `ChainSystem` if the system is in a chain, or `None` otherwise. This could also be used if we ever add more ways of composing systems.

## What alternative(s) have you considered?

We could provide a `SystemParam` that gives debug info about the previous system in the chain. I don't like this as much.

## Additional context

Would improve the panic messages in #5776.