Add dev specific doc for CloudHarness CLI tools

[aranega]

This PR proposes a documentation for CloudHarness developers, to help to locate and understand how the different part of the projects are working together.

The CloudHarness code base can be really complicated to understand well in the first place, there is a lot of sub-projects and libraries. This documentation aims developers to help them navigate through the source code and understand some concepts in order to be able to fix bugs or extend the various tools present in CloudHarness to implement new features quickly.

Sanity checks:

• [ ] The pull request is explicitly linked to the relevant issue(s)
• [X] The issue is well described: clearly states the problem and the general proposed solution(s)
• [ ] From the issue and the current PR it is explicitly stated how to test the current change
• [ ] The labels in the issue set the scope and the type of issue (bug, feature, etc.)
• [X] All the automated test checks are passing
• [ ] All the linked issues are included in one milestone
• [ ] All the linked issues are in the Review/QA column of the board
• [ ] All the linked issues are assigned

Breaking changes (select one):

• [X] The present changes do not change the preexisting api in any way
• [ ] This PR and the issue are tagged as a breaking-change

Possible deployment updates issues (select one):

• [X] There is no reason why deployments based on CloudHarness may break after the current update
• [ ] This PR and the issue are tagged as alert:deployment

Test coverage (select one):

• [ ] Tests for the relevant cases are included in this pr
• [X] The changes included in this pr are out of the current test coverage scope

Documentation (select one):

• [ ] The documentation has been updated to match the current changes
• [X] The changes included in this PR are out of the current documentation scope

Nice to have (if relevant):

• [ ] Screenshots of the changes
• [ ] Explanatory video/animated gif

[filippomc]

Hey @aranega I see this is still in draft, worth merging in your opinion?

[aranega]

@filippomc I think it's OK, but you should take a look to see if I'm not saying something wrong inside. I don't think it's finished yet, but at the same time, it's something that we can improve with time.