[CCXDEV-10215] CI: Use openapi-generator-cli docker image instead of installing it

[epapbak]

Description

Use the docker image provided by the OpenApiTools organization instead of installing the openapi-generator-cli every time a PR is verified.

The installation seems to fail quite often due to downtimes of the repository used to verify and download the jar file used by the verification tool.

The issue does not seem to have been fixed yet. See OpenAPITools/openapi-generator-cli#680 and OpenAPITools/openapi-generator#9349. So using the docker image allows us to use the tool without interacting with the "failing" repository.

Fixes CCXDEV-10215

Type of change

• Bug fix (non-breaking change which fixes an issue)

Testing steps

CI

Checklist

• make before_commit passes
• updated documentation wherever necessary
• added or modified tests if necessary
• updated schemas and validators in insights-data-schemas in case of input/output change

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (cff2d4c) 73.46% compared to head (5234027) 73.46%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #498   +/-   ##
=======================================
  Coverage   73.46%   73.46%           
=======================================
  Files          11       11           
  Lines         603      603           
=======================================
  Hits          443      443           
  Misses        135      135           
  Partials       25       25           

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[epapbak]

/retest

[tisnik]

ok let's try this