AI-173: Support !include in yaml config files

[efunneko]

This adds the ability to do:

!include my_stuff_at_root.yaml

my_obj:
  !include my_sub_object.yaml

This will copy the specified file (relative to current file) into the current file and do this recursively. If the !include directive is indented, then that amount of space will be added to each line of the inserted file.

[gitstream-cm]

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[sonarqube-solacecloud]

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