re-use global_pattern

[hramoser]

Do not move global_pattern_opt to allow use for multiple sinks.

[codecov-io]

Codecov Report

Merging #20 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   87.99%   88.01%   +0.02%     
==========================================
  Files           3        3              
  Lines         408      409       +1     
==========================================
+ Hits          359      360       +1     
  Misses         49       49

Impacted Files	Coverage Δ
include/spdlog_setup/details/conf_impl.h	89.29% <100%> (+0.03%)	⬆️

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[guangie88]

@hramoser Thank you for the PR!