bloat probe (and others): reduce frequency

[Krysztophe]

The bloat query runs much too often. The bloat should not evolve very much in 60s.

On my experimental setup, the bloat query runs thousands of times in a day. Some databases have thousands of tables or partitions, and the query may need some times 10 or 20s to finish (typical is <200ms). This isn't a typical setup but that can happen.

Suggestion: add a parameter to modify the frequency of some/most/each probe at will and add a less frenetic default.