detect: add configurable limits for datasets

detect: add configurable limits for datasets

Ticket: 7615

Avoids signatures setting extreme hash sizes, which would lead to very
high memory use.

Default to allowing:
- 65536 per dataset
- 16777216 total

To override these built-in defaults:

```yaml
datasets:
  # Limits for per rule dataset instances to avoid rules using too many
  # resources.
  limits:
    # Max value for per dataset `hashsize` setting
    #single-hashsize: 65536
    # Max combined hashsize values for all datasets.
    #total-hashsizes: 16777216
```