replace go-junit-report with gotestsum

[electricmonk]

We spend 40 seconds in each build job to download go-junit-report, which is used to convert go test output to junit xml format readable bi circleci.

There's another tool, gotestsum which also supports this, which is available on all circleci machines.

Consider making the switch. @amir-arad already did that in https://github.com/orbs-network/boyarin

[amir-arad]

gotestsum is built into circleci go docker image, not the machine.
technically I only use gotestsum in boyar E2E, which uses machine, so I have to install it explicitly as part of setting up the machine (in addition to re-installing go and nodejs)
see here

using it in a docker image should be a breeze, I just didn't get there yet.