Allow overriding branches for non default repositories in YML specs

Currently, it is only possible to override a branch for a default repository https://docs.atlassian.com/bamboo-specs-docs/7.1.1/specs.html?yaml#overriding-branch-of-a-linked-repository.

It would be great if it was possible to do the same for non default repositories in the plan using specs, i.e. specify repo name and branch in yaml.

Note: Java Specs have this functionality