## Checklist
- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/2158
- [x] if you changed anything related how experiments work and you need to reflect these changes in the ooni/spec repository, please link to the related ooni/spec pull request: https://github.com/ooni/spec/pull/250
## Description
This diff refactors the codebase to reimplement tlsping and tcpping
to use the step-by-step measurements style.
See docs/design/dd-003-step-by-step.md for more information on the
step-by-step measurement style.
This pull request publishes the step-by-step design document that I have been discussing with @hellais and @DecFox recently. Compared to the document that was approved, this one has been edited for readability.
While there, I figured it was also be beneficial to publish the few ooni/probe-cli related design documents we produced in the past, because they probably help someone to get acquainted with the codebase.
Reference issue for this pull request: https://github.com/ooni/probe/issues/2148
