misc: Auto retry PDF generate jobs in case of HTTP errors

[vincent-pochet]

Context

From time to time some Invoices::GeneratePdfJob are failing with the following error:

HTTP 503 - URI: http://pdf-web.default.svc.cluster.local/forms/chromium/convert/html. Error: Service Unavailable

Since to fix the issue we usually just have to retry the job, the retry could be automated.

Description

This PR adds a retry_on attribute for LagoHttpClient::HttpError for 6 attemps with exponnential wait time between each retry.