Sentry integration for Nextcloud

All this app needs to operate is a valid Sentry DSN. You can set it via the command line
```bash
php occ config:system:set sentry.dsn --value=https://xxxxx:yyyyy@sentry.io/1234567
```
or add the entry directly to `config/config.php`
```
"sentry.dsn" => "https://xxxxx:yyyyy@sentry.io/1234567"
```