Add sum to CI Pipeline logger

What does this MR do and why?

When trying to see the percentage of time spent in each section, "avg" can be misleading. With "sum", we can see the total time spent in that section.

For example; I created a chart that displays the percentage of time spent in each section of lib/gitlab/ci/config/external/mapper.rb. However, I had to use avg so that it may have the wrong result due to nested includes.

I created this MR because we want to see the details of config_mapper_process #367899 (closed).

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