Make Gradle task GenerateTask less verbose

[BraisGabin]

This PR is related with #8982 but it doesn't fix it. Each time that I execute the GenerateTask from gradle I get this output:

Cleaned up output directory /path/build/generated/swagger before code generation (cleanupOutput set to true).
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Successfully generated code to /path/build/generated/swagger

I get that the donation message is a sensible topic but I think that it's ok to hide the messages "Cleaned up output directory..." and "Successfully generated code to..." behind the current verbose flag. Tha's what this PR does.

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