Reduces pool_params::ping_interval default from 1h to 10s

[anarthal]

Improves the detection of broken connections to reduce the chance of handing over broken connections.

close #510

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.17%. Comparing base (0661a2b) to head (833bb6d).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #512   +/-   ##
========================================
  Coverage    99.17%   99.17%           
========================================
  Files          146      146           
  Lines         7405     7405           
========================================
  Hits          7344     7344           
  Misses          61       61           

Files with missing lines	Coverage Δ
include/boost/mysql/pool_params.hpp	100.00% <ø> (ø)

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