Cortex drops the `limit` field in the Rule Group

[emanlodovice]

Describe the bug
https://prometheus.io/docs/prometheus/latest/configuration/recording_rules/#rule_group prometheus rule groups has a field limit. Cortex accepts this field in the CreateRuleGroup API but when you list the rules the limit is not there. From the code it seems like cortex is not storing the limit field.

To Reproduce
Steps to reproduce the behavior:

1. Create a rule group with limit set.
2. Call ListRules and the limit field is not there.

Expected behavior
Cortex support limit field in the rule group.

Additional Context