Pipe function support for config vars

Łukasz Soszyńskirequested to merge
config-vars-support-for-pipe-functions into main

This MR is needed to implement search-guard/search-guard-suite-enterprise#57 (closed)

The following features are introduced

  • support for pipe functions in config vars, e.g. #{file:/tmp/my_file.tmp|toLowerCase}
  • added pipe function base64
  • it is possible to inject custom pipe functions via Parser.Context

Merge request reports

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