support custom secret in tekton results

[jkandasa]

Changes

For now there is no way to supply S3 credentials into results api pod via secrets. This PR optionally injects those references via environment variable into tekton-results-api deployment.
As these values are injected as environment variable takes the higher precedence.

There is an issue in results repository about this: tektoncd/results#469, tektoncd/results#432

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Run make test lint before submitting a PR
• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Commit messages follow commit message best practices

See the contribution guide for more details.

Release Notes

To get `S3` credentials from secret, a new property called `secret_name` added under TektonResult spec. User can create a secret with `S3` credentials and update the secret name in `secret_name` property.

[jkandasa]

/cc @khrm

[tekton-robot]

@jkandasa: GitHub didn't allow me to request PR reviews from the following users: khrm.

Note that only tektoncd members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to this:

/cc @khrm

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/kubernetes/tektonresult/transform.go	66.7%	69.1%	2.4

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

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[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/kubernetes/tektonresult/transform.go	66.7%	69.1%	2.4

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/kubernetes/tektonresult/transform.go	66.7%	69.1%	2.4

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/kubernetes/tektonresult/transform.go	66.7%	70.9%	4.3

[jkandasa]

cc @piyush-garg @PuneetPunamiya @khrm

[piyush-garg]

Issue on results tektoncd/results#432

[piyush-garg]

/lgtm

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/kubernetes/tektonresult/transform.go	66.7%	70.9%	4.3

[piyush-garg]

/lgtm