Added frequency capping constraints to the personalized offer schema

Frequency capping constraints define additional rules based on prior offer proposition, either across all audiences or for a particular profile identity.

## What are the schemas that are affected by the issue

https://github.com/adobe/xdm/blob/master/extensions/adobe/experience/offer-management/personalized-content-offer.schema.json

## What are examples of products that are impacted by the issue

No impact on the existing products. Frequency capping constraints define additional rules based on prior offer proposition, either across all audiences or for a particular profile identity.

Open extensions/adobe/experience/offer-management/personalized-content-offer.schema.json and read the existing personalized offer structure first. Add the frequency capping constraints described in the issue for rules applying across all audiences and for a particular profile identity, then verify the schema remains valid.

Written by the indexing model from the issue text.