AWS system test example_dynamodb_to_s3: add retry when fecthing the export time

[vincbeck]

AWS Dynamodb UpdateContinuousBackups API is not stable and we need to add a retry logic when calling update_continuous_backups. The API might return Backups are being enabled for the table: <...>. Please retry later.

As long as I dont like doing that, we have no choice since the API behavior is not stable on the service side ...

---

^ Add meaningful description above

Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in newsfragments.

[vandonr-amz]

ok to let it go like this, but I'd prefer it without the random.

[vincbeck]

Thanks for the feedbacks guys, it made me look if any library was already used for such purpose and there is one: tenacity. I removed the custom implementation and now use this library. It should address all your concerns.

[o-nikolas]

Approved, but I'll hold off merging since there is a broken static check making the build go red.

[ferruzzi]

@o-nikolas and @vincbeck the CI is green on this one, do you need another review on it or is it good to go?

[o-nikolas]

@o-nikolas and @vincbeck the CI is green on this one, do you need another review on it or is it good to go?

Nope, I've just been merging/retrying/waiting for it to be green today. I'll merge now :)