refactor!: remove SetOperatorParams in favor of MsgJoinService (#128)

## Description

Closes: MILK-97
Depends-On: #126 

This PR is a continuation of #126 where I extract the `JoinedServiceIDs`
from `OperatorParams` in order to store them insidea `collection.map`
where the key is the operator id and the value is the list of services
being secured by the operator.

---

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