Fix / consistent usage of f-strings

[riccardoporreca]

Follow-up from #526

• Fix missing f for massage strings with placeholders otherwise unresolved.
• Favor f-strings over .format() when sensible to do so.
• Replace %-formatting with f-strings.

[baszalmstra]

You could also consider running: https://github.com/asottile/pyupgrade

But that won't catch the many errors you fixed as well! :)

[riccardoporreca]

I have actually found and used a flake8 plugin https://pypi.org/project/flake8-use-fstring/ to easily spot % and .format().

[codecov-commenter]

Codecov Report

Merging #538 (bf69d64) into main (d63e2f1) will decrease coverage by 1.10%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##             main     #538      +/-   ##
==========================================
- Coverage   83.11%   82.01%   -1.11%     
==========================================
  Files          78       78              
  Lines        5936     5977      +41     
==========================================
- Hits         4934     4902      -32     
- Misses       1002     1075      +73     

Impacted Files	Coverage Δ
quetz/authentication/auth_dao.py	90.00% <ø> (ø)
quetz/database_extensions.py	60.00% <ø> (ø)
quetz/db_models.py	96.89% <ø> (ø)
quetz/main.py	86.70% <ø> (-2.29%)	⬇️
quetz/tasks/reindexing.py	83.67% <ø> (ø)
quetz/versionorder.py	95.49% <0.00%> (ø)
quetz/authentication/jupyterhub.py	91.93% <100.00%> (ø)
quetz/dao.py	91.08% <100.00%> (ø)
quetz/jobs/runner.py	90.47% <100.00%> (ø)
quetz/tasks/indexing.py	92.10% <100.00%> (+0.32%)	⬆️
... and 3 more

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[riccardoporreca]

@wolfv, @baszalmstra, I am coming back to this: I have included the flake8-use-fstring plugin and changed an additional occurrence of .format.
I have checked whether the main branch might have introduced meanwhile similar issue with unresolved placeholders (not detectable by the plugin) and could not find any such instance.