Upgrade circle-ci config to v2.1

[sspaink]

Required for all PRs:

• Signed CLA.

Updated circle-ci config to use version 2.1, allows us to benefit from new config management features.
Good overview of the changes with this new version: https://discuss.circleci.com/t/circleci-2-1-config-overview/26057

• I replaced the YAML anchors in the beginning of the file with "executors", making the syntax looks cleaner.
• I added "commands" to reduce duplication in the job definitions
• Added a small shell script in scripts/ to execute a circle-ci job locally, more info here: https://circleci.com/docs/2.0/local-cli/
• I removed the underscore separator used in the int literal in the sumologic plugin, not happy with this change because it is valid Go since 1.13, but for some reason the circle-ci cmd line tool fails due to this line. The error: expected ';', found _000_000 (and 3 more errors) Luckily the underscores are just syntactical sugar and removing them does let the number match the README.
• I also changed the job names to use underscores instead of periods because v2.1 is more picky and complains

The orbs feature might also be beneficial in a future change, there is a Go one that provides caching features: https://circleci.com/developer/orbs/orb/circleci/go but I didn't add it in this change.