1.0 to 2.0 upgrade path

This is an initial upgrade path. It doesn't cover views or page manager. Also people who might have implemented the approach to add an extras column for as recommended in v1 are not taken into account.

My last commit adds `entity_id` in the legacy schema to ensure that it stays as string. In #3270630 it was update to be an integer due to performance reasons but I would like us to keep it as string in the legacy plugin for this initial update path then open a follow up issue if the people who were using V1 face the performance problem.

Thanks Nia for the great work. This patch works for me as excepted for my use case, working with the legacy plugin to use my data from version one.

Howeveer I found two potential issue which worth to discuss:

1. When I enable the generic usage data and the generic usage data counter in plus the legacy plugin I have this exception:

if (!$database_schema->fieldExists($table, $counterField)) {
  throw new \Exception('Usage Data table ' . $table . ' schema should have a counter ' . $counterField . ' column.');
}

Line 77 in srcUsageDataDatabaseStorage.php
I think we need to test more to see how to have them all enabled without issue.

2. I noticed when I visit/view a page where I have a media (I have a video) the module is adding the event_type download for the entity_type_id media row, it should be just 'view'
I think this may be an issue for the version 2 of he module.

Thanks.

Thank you for working on this upgrade path! Committed.

Automatically closed - issue fixed for 2 weeks with no activity.