Fix EZP-22065: Make SiteAccess a synchronized service

https://jira.ez.no/browse/EZP-22065

[Specifications can be found here](https://github.com/ezsystems/ezpublish-kernel/blob/a7d5f3a1d3dec5155ded8ddd71dbb75a45644550/doc/specifications/siteaccess/synchronized_siteaccess.md).