Issue #1337 Child device support for c8y-config-plugin

[albinsuresh]

Proposed changes

Extend c8y-config-plugin to support c8y_UploadConfigFile and c8y_DownloadConfigFile operations on child devices

Types of changes

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• [ ] Documentation Update (if none of the other choices apply)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

Checklist

• [x] I have read the CONTRIBUTING doc
• [x] I have signed the CLA (in all commits with git commit -s)
• [ ] I ran cargo fmt as mentioned in CODING_GUIDELINES
• [ ] I used cargo clippy as mentioned in CODING_GUIDELINES
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)

[cmosd]

Hi, here is a draft of what is implemented so far for #1337

• [x] config update
• [x] config upload
• [x] bootstrap

What is still left to do is the following:

• [ ] OperationStatus::Updated (implement Updated in all other places OperationStatus is used in the code base)
• [ ] refactoring of paths (/etc/), removing unused tmp_dir, adding comments, unwraps
• [ ] tests?
• [ ] clippy
• [ ] update python script
• [ ] unused dependencies