config extension

Need to add functionality of configs's extension 

1. local
```
extends:
  path: parent_config.yaml
```
2. remote
```
extends:
  get:
    url: "{{.vars.REPO_1}}/raw?ref=master"
    headers:
      PRIVATE-TOKEN: glpat-VyzoK6TK6Y7iodsYA_zH
```

configs's extension functionality have to override parent config  tags with considering child config tag