[Docker Compose] Support `configs` in local Compose mode.

[thirdgen88]

Tell us about your request
Docker Compose running against local context should support configs declaration similar to how secrets is supported for local Docker Compose.

Which service(s) is this request for?
Docker Compose

Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?
I've enjoyed that I can use similar syntax in my Compose files between Swarm and Local modes. It feels natural that configs should be supported since secrets works and is a very similar function.

Are you currently working around the issue?
We can fallback to a bind-mount volume of a given config file in place of a configs declaration.

Additional context
Existing issue #937 was created in docker/compose-cli.

[chris-crone]

Thanks for the feedback @thirdgen88!

We an issue tracking this for the Compose CLI. No ETA but it shouldn't be hard to implement.