Set a rule limit on ProcessScanResultPolicyService

As discussed in this MR(!76595 (merged)). Setting a limit to the amount of rules is important prior to enabling this feature flag.

And as proposed in !76595 (comment 802561635) , we will limit each policy to 5 rules summing a total of maximum of 25 rules per repository.

Implementation plan

• backend Add limit as part of the process scan result jobs.
• backend And/or add the limit on the schema file.
• documentation Update this information as part of the policy documentation