[Feature Request] Add option to replace "/" in hydra.job.override_dirname

[stefangstark]

If overrides contain a / then a subdirectory is created when using hydra.job.override_dirname. The referenced discussion suggests to write a custom function that replaces instances of /. However, it would be convenient if this was done using a mechanism similar to e.g. hydra.job.config.override_dirname.kv_sep.

Discussed in #2409

^{Originally posted by Aceticia October 9, 2022}
I'm using the override_dirname as the folder to store checkpoints and logs. This does store the logs, but since my configs contain overrides with /, hydra ended up not treating them as part of the subdir but as a directory under the subdir, creating one redundant level of folder each time I override something. This is a pretty small inconvenience, and it would probably be very difficult to fix (how to differentiate where user actually want a subdirectory but not override?), but I imagine it's not the intended behavior?

For more details, here is how I'm overriding some configs. If there is an alternative where I can just not use / overrides I guess that would solve the issue too.

models
- default.yaml
- temporal_nets
    - net1.yaml
    - net2.yaml

In net1.yaml and net2.yaml, there are configurations for neural networks including __target__ instantiations and their hyperparameters. In default.yaml I simply have a default list of using net1.yaml. When I do need to run an experiment with net2, I just override with models/temporal_nets=net2. What are alternative ways to organize the configs, so that I can override the choice of temporal_nets? Any suggestions would be appreciated. Thank you.