Expose performance options (v0.20)

[lcarva]

Changes

This allow admins to specify a few parameters to better suit their use of Chains.

--threads-per-controller controls the number of concurrent threads the Chains controller processes. The default value is 2.

--kube-api-burst controle the maximum burst for throttle.

--kube-api-qps controles the maximum QPS to the server from the client.

The approach taken here is the same one used by the Tekton Pipeline controller for the sake of consistency in the ecosystem.

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Release Notes

Expose new performance parameters to control controller's execution. See docs at https://tekton.dev/docs/chains/performance for details.

[chitrangpatel]

/approve
/lgtm

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