fix(python-sdk-generation): display actual error message when SDK generation fails

[siddhuwarrier]

Previously, we were not returning the outputs sent by cmdline tools to stderr back to our
application, as a result of which when a command failed, we could not tell exactly what was going
wrong. Fix that so we can quickly fix underlying issues.

Old error message:

 ERROR   Error generating Python SDKexit status 1

New error message (for example):

  ERROR   Error generating Python SDKError: exit status 1.
          SDK Output: Exception in thread "main" org.openapitools.codegen.SpecValidationException: There were issues with the specification. The option can be disabled via validateSpec (Maven/Gradle) or --skip-validate-spec (CLI).
           | Error count: 3, Warning count: 0
          Errors:
                -attribute paths.'/v1/msp/inventory/devices/ftds/upgrades/runs/{mspUpgradeRunUid}'(get).operationId is repeated
                -attribute paths.'/v1/msp/inventory/devices/ftds/upgrades/runs/{uid}'(delete).operationId is repeated
                -attribute paths.'/v1/msp/inventory/devices/ftds/upgrades/runs'(get).operationId is repeated

                at org.openapitools.codegen.config.CodegenConfigurator.toContext(CodegenConfigurator.java:717)
                at org.openapitools.codegen.config.CodegenConfigurator.toClientOptInput(CodegenConfigurator.java:744)
                at org.openapitools.codegen.cmd.Generate.execute(Generate.java:527)
                at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
                at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)