Push build/test statistics to elastic

[msimberg]

#891 pushes performance data to elastic. We should expand this to push general metrics about the builds:

• [x] test pass/fail (#907)
• [x] test time (this gets us header build times as well, #907 and #952)
• [ ] build times
• [x] file sizes (#958)

I think most of this would be possible to add by sending the CTest/CMake XML output, transformed to json (using https://github.com/kislyuk/yq#xml-support?), to elastic.