Support build.cache_from in docker-compose manager

[wolfgangwalther]

What would you like Renovate to be able to do?

In a docker compose file, there can be a list of docker images in build.cache_from. Example from the docs:

build:
  context: .
  cache_from:
    - alpine:latest
    - corp/web_app:3.14

It would be great if renovate could update those, too.

If you have any ideas on how this should be implemented, please tell us here.

Extend the docker-compose manager to support extracting build.cache_from.

Is this a feature you are interested in implementing yourself?

No

[viceice]

should be easy to implement