Doctor and patient assignment

As a patient or a doctor I want to be able to assign each other (patient + doctor, doctor + patient) so that we can make sure to have a secure and reliable way of sharing a treatment plan to use for the insulin dosage calculation.

Context

In order to properly assign doctors and patients, this process needs to be safe so we can make sure there are no mistakes. This means that the assignment needs to be done two ways so we can make sure two set of eyes have reviewed it. If there is an error in this process, it would mean that people could potentially get the wrong insulin dosage (fatal).

In scope

add in app confirm page to assign a doctor
add in frontend add patient page to begin the adding process
the confirmation will happen based on a randomly generated code
the overall orchestration of the assignment the backend will do

Out of scope

Any QR code scanning to make this easier, this will be handled in https://github.com/diabetes-assistant/documentation/issues/52

Tech notes

Add the required ui in frontend and app
Add a route that handles this functionality in backend
this should set the state of an assignment in the backend first to new, then to patient confirmed, then to overall confirmed when doctor confirms
in the app it would be nice if you could display already some information if the given code is correct (see sketch)
the code should be randomly generated of 6 letters and numbers (alphanumerical), this needs to be data of the assignment when created
in the app, start showing preview data as soon as the letters have reached 6 digits, not before, do not show anything if the code is invalid, only on button press show snackbar with invalid hint
in the app make the confirm button not clickable, unless more than 5 digits are present in the confirmation field