add child device tutorial

[hansb001]

Signed-off-by: Hans Boef hansboef@gmail.com

Proposed changes

Adding a tutorial for child device config management.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• 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

• I have read the CONTRIBUTING doc
• 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)

Further comments

[albinsuresh]

The following doc-wide changes are also required:

1. Replace references to "child device agent" and "agent" with "child device connector" and "connector"
2. It's a good markdown doc practice to keep multiple sentences in a paragraph across multiple lines instead of keeping them together. This makes the suggestions easier during reviews.
3. Add images of the Cumulocity UI in relevant sections.

[albinsuresh]

The following things must be taken care of, at a doc level, before the next iteration:

1. Use the admonish blocks as documented here for both Notes and Examples
2. When accept commit suggestions, use the batch accept feature of github to avoid commits for each and every line as shown:
   
3. Make sure that the markdown document renders properly, especially for numbered list items. There were many such numbering issues in the current version.
4. Double check the links in the rendered version as some of my suggested headline changes will have an impact on these links as well.

[albinsuresh]

@hansb001 Made the following major changes in my last commit:

1. Fixed the indentation of all examples and images
2. Changed the admonish blocks used for examples to simple console blocks for better formatting
3. Re-ordered and updated some content

[reubenmiller]

Approved