Prepare utility for scripts

[MrOrz]

We are introducing multiple scripts for category review & user blocking mechanism in future PRs (such as #265, #267).

This PR adds preparations for those scripts and is organized to a separate PR to make the size of future PRs more managable.

Added in this PR:

• Install cli-progress to display progress in cli scripts (actually used in PRs like #265, #267)
• Align github CI node version with the one in Dockerfile
• Extract getAllDocs() (an async generator to walk through all matching docs in an ES index) to a separate utility function

[coveralls]

Coverage decreased (-0.009%) to 86.235% when pulling b4118e97e4dbcd525c23f9d88296c7e390b08e48 on scripts-utils into 8f0d1dde60afc432a1d43baef9ed21c1dfa58c2c on master.