JSON Pretty Format Completed Requests in cbcollect_info

In 7.0+, the system:completed_requests catalogue is collected as part of a cbcollect_info log collection by default for Query Service nodes. This is collected to completed_requests.json.

This file doesn't have JSON indentation which makes it difficult to read at a glance. Only a small factor, but it would make it easier to review this file if it were converted to pretty JSON format as part of the log collection (ie. the file is given JSON indentation). 

This would prevent us from needing to do something like the following after unzipping a cbcollect_info log archive to get this file in a more readable format:

jq . completed_requests.json > completed_requests.txt