Enhance QueryRecorder to support finding queries by source + memoizing of read only attributes

What does this MR do?

https://docs.gitlab.com/ee/development/query_recorder.html

1. Enhance QueryRecorder to collate DB calls by their source.
2. Memoize read only attributes.

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

As I see now, this class is only used and doesn't have any tests of its own.

It should actually be straight forward to test it, I'll add some tests to cover old and new features.

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers