Currently, there are some useless includes in the codebase. We can use a tool named include-what-you-use to optimize these includes. By using a strict include-what-you-use policy, we can get lots of benefits from it.
#5146
Add histogram metrics into util/metrics.h. The data structure of histogram is implemented in util/histogram.h,
which could also be used in other situations that in need of histogram. Unit tests added as well.
