InitContainer should take GIT credentials from `kind: Secret`

Actual:

```bash
  initContainers:
  - args:
    - checkout
    - https://zzzzzzzzzzzzzzzz
    - --path
    - /var/www/riotkit/wp-content/themes/yyyyyyyy
    - --rev
    - master
    - --token
    - xxxxxxxxxxxxxxxxxxx
    - --username
    - __token__
```

Expected to replace `xxxxxxxxxxxxxxxxxxx` with e.g. `$GIT_TOKEN`