Fix too many open files on file system

[quambene]

Fix too many open files on file system:

• Set the default for max_idle_connections_per_host in settings.json from 100 to the more sensible 10. Idle connections were stuck in the connection pool.
• Idle connections will be removed after 5 seconds (see idle_connections_timeout in settings.json).

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (9a6ff33) 90.63% compared to head (7ac66c5) 90.55%.

Files	Patch %	Lines
src/cmd/fetch.rs	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #62 +/- ## ========================================== - Coverage 90.63% 90.55% -0.09% ========================================== Files 31 31 Lines 4059 4064 +5 ========================================== + Hits 3679 3680 +1 - Misses 380 384 +4 ```

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