Add push mode for prometheus monitor

[fishpenguin]

#813

[codecov]

Codecov Report

Merging #905 into master will decrease coverage by 0.03%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master     #905      +/-   ##
==========================================
- Coverage   88.57%   88.54%   -0.04%     
==========================================
  Files         308      296      -12     
  Lines       13335    13164     -171     
==========================================
- Hits        11812    11656     -156     
+ Misses       1523     1508      -15

Impacted Files	Coverage Δ
core/src/server/Config.h	100% <ø> (ø)	⬆️
core/src/metrics/prometheus/PrometheusMetrics.h	87% <0%> (-1.4%)	⬇️
core/src/db/DBImpl.cpp	86.61% <100%> (-1.44%)	⬇️
core/unittest/server/test_config.cpp	100% <100%> (ø)	⬆️
core/src/server/Config.cpp	83.25% <86.66%> (-9.83%)	⬇️
core/src/wrapper/WrapperException.h	0% <0%> (-100%)	⬇️
core/src/wrapper/WrapperException.cpp	0% <0%> (-100%)	⬇️
core/src/scheduler/job/BuildIndexJob.h	50% <0%> (-50%)	⬇️
core/src/scheduler/optimizer/FallbackPass.cpp	66.66% <0%> (-33.34%)	⬇️
core/src/utils/Exception.h	75% <0%> (-25%)	⬇️
... and 33 more