Get merged profiles of all the instances of a service

[shaheerem]

Here's the PR for the feature: #403

I've added new test cases, and ran the old ones, all are passing.

This feature modifies the GET endpoint of profile, which was not implemented before, it will now first fetch the profiles of the given service name, merge them all together, and provide with the merged result.
This feature is handy where you need to calculate the distributed coverage of various services.

Kindly review the PR and let me know if there's anything to change, I will make the changes as well.