Avoid exposing the Postgres credentials

[sbivol]

Quetz prints the database connection string on startup. This is unnecessary and potentially insecure, since the person reading Quetz logs is not necessarily authorized to manage Quetz.
This patch replaces the connection string with just the name of the database engine: SQLite, PostgreSQL, or whatever happens to be preceding the first slash (useful in case the user made a typo, or other DB engines become supported in the future).

[codecov-commenter]

Codecov Report

Patch coverage: 77.77% and project coverage change: -1.00 ⚠️

Comparison is base (1f29a9c) 82.28% compared to head (ce5a6e6) 81.28%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #628      +/-   ##
==========================================
- Coverage   82.28%   81.28%   -1.00%     
==========================================
  Files          78       78              
  Lines        6124     6130       +6     
==========================================
- Hits         5039     4983      -56     
- Misses       1085     1147      +62     

Impacted Files	Coverage Δ
quetz/cli.py	74.68% <77.77%> (-0.16%)	⬇️

... and 3 files with indirect coverage changes

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[wolfv]

Thanks!