Add an new origin visit info model object and related backend api

Upsert and Read methods

Related to #2443 (closed)

Test Plan

tox

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Migrated from D4838 (view on Phabricator)

sql/updates/19.sql

+insert into dbversion (version, release, description)
+       values (19, now(), 'Work In Progress');
+
+create table origin_visit_stats (
+  url text not null,
+  visit_type text not null,
+  last_eventful timestamptz,
+  last_uneventful timestamptz,
+  last_failed timestamptz,
+
+  primary key (url, visit_type)
+);
+
+comment on column origin_visit_stats.url is 'Origin URL';
+comment on column origin_visit_stats.visit_type is 'Type of the visit for the given url';
+comment on column origin_visit_stats.last_eventful is 'Date of the last eventful event';
+comment on column origin_visit_stats.last_uneventful is 'Date of the last uneventful event';
+comment on column origin_visit_stats.last_failed is 'Date of the last failed event';