Expose performance options

[lcarva]

Changes

This allow users to specify the number of concurrent threads the Chains controller processes. The default value is 2 which is not realistic for large deployments.

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

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• [x] Has Docs included if any changes are user facing
• [ ] Has Tests included if any functionality added or changed
• [x] Follows the commit message standard
• [x] Meets the Tekton contributor standards (including functionality, content, code)
• [ ] Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings)
• [ ] Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

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

[tekton-robot]

The following is the coverage report on the affected files. Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/taskrun/controller.go	88.9%	89.5%	0.6

[tekton-robot]

@vdemeester:

In response to [this](https://github.com/tektoncd/chains/pull/1079#pullrequestreview-1946489844): >/meow Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chitrangpatel, vdemeester

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[vdemeester]

@chitrangpatel @lcarva can we also backport this to a few previous release ? 🙏🏼

[chitrangpatel]

/lgtm