Share search path checks and add a console report

Problem

This MR introduces new rake task db:diagnostics to allow users to use console for diagnostics verifications.

It does not require GitLab instance to be working and an many cases simplifies support engineers work.

Changes

1. Refactor the old diagnostics code - keep only display logic in views, no checks. All the business logic now in Ruby files and easy to reuse.
2. Add new rake task to display diagnostics
3. As the amount of displayed information expected to be significant, output is interactive

Non interactive output version can be added later if needed (for example by directing output to a text file)

Sample output

References

#603104 (closed)