Add possiblity to add the scroll batch size to reactive code

[sothawo]

Currently there is no possibility to set the size of the single requests that are sent to the cluster when scrolling through all records (see #2023), the current code always uses the max number of 10.000.

It should be possible to set this for a single query or as global value in the configuration.

Imperative code does not have this problem, here the page size is used as there is a dedicated scroll method. Reactive code automatically switches to scroll from normal find when there is no page size or limit set.

[sothawo]

Not adding it as a global configuration value, because every query and entity is different in size, so a global value does not make sense. Default value will be set to 500.