[ML] Get filters size defaults to 10 instead of 100

[dimitris-athanasiou]

Steps to reproduce

1. Create 11 filters
2. Call the get filters API with no additional params

Observed behaviour

This should return all 11 filters that were created

Actual behaviour

Only 10 filters are returned.

[elasticmachine]

Pinging @elastic/ml-core (:ml)