Switch ruby client to use openapi-generator

[ackintosh]

• Related issue : migrate from swagger-codegen to openapi-generator #93
• Similar PR on the python client : feat: switch python client to use openapi-generator #97

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[ackintosh]

There're hand-written test codes in spec folder, which is deleted on regeneration.

The hand-written tests is deleted on re-generation · Issue #29 · kubernetes-client/ruby

[brendandburns]

close/re-open to trigger CLA bot.

@ackintosh thanks for doing this. I LGTM'd your other PR.

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ackintosh, brendandburns

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[ackintosh]

@brendandburns Thanks for your merging. I'll file a PR to kubernetes-client/ruby to update the client.

[cjwagner]

/hold
Holding this PR because it is a draft PR and is causing problems with Tide.

[brendandburns]

@ackintosh can you remove the 'draft' label?

Thanks!

[ackintosh]

Thanks for notifying me! Made this PR to ready.

[ackintosh]

Thanks for merging this PR. As a next step to migrate to openapi-generator, I'll file a PR to kubernetes-client/ruby in order to update the Ruby client.