Improve R2DBC DatabaseClient documentation regarding array/Collection-like bind parameters

[mp911de]

Based on spring-projects/spring-data-r2dbc#474, the documentation showing usage of Collection-like bind parameters leads to an assumption, that collection values can be used also for updating array columns.

We should clarify by adding a note that R2DBC doesn't support Collection-like values and this feature is solely a Spring feature. We also should mention that inserting/updating array-typed columns (as in Postgres) requires an array-type that is supported by the R2DBC driver, which are typically Java arrays (e.g. String[] to update a text[] column instead of using Collection<String>).

I can submit a pull request to update the docs.