Wordpress-Multisite: Can not migrate data other than the first site's one

Nobody has claimed this yet.

For Wordpress-Multisites with "Matomo for WordPress", each site has a different database table prefix (like wp_matomo_, wp_2_matomo_, ...).
For each table wp_X_matomo_site, there is one single entry (therefore Matomo's idsite is always 1 for each multisite site)

Therefore it is not possible to migrate other than the main site of the multisite, because idsite 2 etc. is not found.

A quick-and-dirty workaround is, to replace the database table prefix, for example with an additional parameter in [Commands/Migrate.php:configure()](https://github.com/matomo-org/plugin-Migration/blob/5.x-dev/Commands/Migrate.php#L21):

```
$this->addRequiredValueOption('source-wpsite', null, 'Source Multisite Site ID you want to migrate');
```

and add in [Commands/Migrate.php:doExecute()](https://github.com/matomo-org/plugin-Migration/blob/5.x-dev/Commands/Migrate.php#L46):

```
$multiSiteId = (int) $input->getOption('source-wpsite');

if($multiSiteId != 1) {
\Piwik\Config::getInstance()->database['tables_prefix'] = str_replace("wp_", "wp_" . $multiSiteId . "_", \Piwik\Config::getInstance()->database['tables_prefix']);
}
```

**_Warning_:** Keep in mind, that this snippet is for demonstration only. The table-prefix might not be "wp_", because it is configurable as well. Also it might be the optimal place and/or way to fix that behavior, as I'm currently not too familiar with Matomo's codebase

Start by reading Commands/Migrate.php, especially configure() and doExecute(), and trace how the database table prefix is selected for migrations. Verify how a configurable WordPress multisite prefix can target a non-primary site without breaking the default case. Done means data from a selected multisite site can be migrated, not only the first site.

Written by the indexing model from the issue text.