Lockable resource plugin can't be configured via CASC.  It seems due to violation of "Rule 1: don't write code for data-binding" from https://github.com/jenkinsci/configuration-as-code-plugin/blob/master/docs/REQUIREMENTS.md 

Auto generated documentation (at <jenkins-host>:configuration-as-code/reference) contains mention of 'lockableresourcesmanager' entry and nothing more.

Configuring it manually and exporting its configuration gave also nothing exported.