Fix bug suggestions with PostgreSQL

[vrigal]

Closes #7986

This PR adds a unit test that reproduce the bug suggestion described by @Archaeopteryx in #7986 that appeared when switching prototype database to Postgresql.

It turns out we cannot rely on Postgresql Full-Text search capabilities for this use-case, as we are trying to mostly match filenames or paths with special characters like slashes or underscores, but postgresql search functions are optimized for tokenization with specific languages instructions (basically we do not search for english...).

So we had to reproduce the Mysql implementation:

1. using pattern matching with ILIKE clause
2. then trigram similarity to get a ranking amongst multiple bugs

⚠️ This requires a specific Postgresql extension to run (available by default)

[vrigal]

@Archaeopteryx Hello.
This is an attempt to reproduce the bug where no bug is fetched with PostgreSQL, described in #7986.
It is not finished yet (it seems the test passes with postgres actually), I will continue working on this on monday.

[Archaeopteryx]

Thank you for the fast fix.

There are some cases which still don't get a suggestion despite the search with a test name and the bug in the database. Example 1 and Example 2.
Could you take another look?
The affected tests all have a - in their name, as far as I can see.

[vrigal]

@Archaeopteryx I looked as your examples, and updated the test with that bug suggestion match from treeherder.mozilla.org.
Unfortunately, I could not reproduce (the test passes).
I'm actually working on updating tests to make ordering possible by -similarity.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.08%. Comparing base (d8e7f0d) to head (3b40e92).
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7988      +/-   ##
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+ Coverage   77.06%   77.08%   +0.01%     
==========================================
  Files         544      545       +1     
  Lines       26940    26958      +18     
  Branches     3382     3382              
==========================================
+ Hits        20762    20780      +18     
  Misses       6011     6011              
  Partials      167      167              

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[vrigal]

-similarity was due to a minor scoring difference between MySQL and Postgres. I updated the fixture and it looks fine now.
I have no hint about the missing suggestions for now.