http mocking: add count configuration for rules

There are use cases where you expect an mock rule to match at most N times. I would like to be able to control the maximum number of times that an rule may match, and after that quota is reached it will no longer be considered when matching.

Related: https://github.com/elastic/integrations/pull/11773/files#diff-706d6118d9970af245e28ed7da171d2b5070e888148e57d6d989ace49a15f78bR51