Add tutorial showing how to migrate from DynamoDB

[julienrf]

Here is how the tutorials renders in the docs:

[julienrf]

@tarzanek Can we merge this PR please? It can be improved later, e.g. by going a bit further and including the application in the scope of the tutorial (e.g. showing how to migrate the data without turning off the application that uses the data), but the priority for now is to unblock the publication of the blog article.

[tarzanek]

ok, I merged but I wanted to say that samples contain optional parameters, e.g. savepoints
that could be cleaned
so yes, let's improve later