Rename NamespaceSettings::UpdateService

Because this service actually does not update the resource (it just sets settings attributes), it would be better to rename this service to make it clear and avoid confusion. Maybe something like NamespaceSettings::SetAttributesService? 🤷

The following discussion from !56397 (merged) should be addressed:

• @jprovaznik started a discussion: (+1 comment)

  In this phase, the group being created is not saved yet - wouldn't calling handle_namespace_settings on this place cause creation/saving of both settings and the group itself? If so, wouldn't it be better to rather take care of updating namespace settings inside the transaction block bellow only if group.save succeeds?