feat(backend): Source ObjStore Creds from Env in Tekton Template

[gmfrasca]

Which issue is resolved by this Pull Request:
Unblocks opendatahub-io/data-science-pipelines-operator#151

Description of your changes:
Cherry-pick feature from upstream kubeflow#1259

Allow admins to define OBJECTSTORECONFIG_CREDENTIALS(SECRET|ACCESSKEYKEY|SECRETKEYKEY) env vars instead of the previously hardcoded mlpipeline-minio-artifact, accesskey, and secretkey values, respectively

Environment tested:

• Python Version (use python --version): 3.11
• Tekton Version (use tkn version): 0.31
• Kubernetes Version (use kubectl version): 1.22
• OS (e.g. from /etc/os-release): Fedora 38

Checklist:

• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[gmfrasca]

/retest

[HumairAK]

/lgtm
/approve

[openshift-ci]

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[HumairAK]

Good way to test this:

1. Deploy dspa via dspo
2. scale down DSPO
3. Add deploy: false to DSP sever in DSPA:

spec:
  apiServer:
    deploy: false

copy the mlpipeline-minio-artifact secret, recreate it with metadata.name: custom-secret, update the accesskey and secretkey KEYS to custom values, delete mlpipeline-minio-artifact, restart pipeline server pod, you'll see it crash because it's missing the secret we just deleted, replace it with a custom secret, add the following env vars to the dsp server deployment:

OBJECTSTORECONFIG_CREDENTIALSSECRET
OBJECTSTORECONFIG_CREDENTIALSACCESSKEYKEY
OBJECTSTORECONFIG_CREDENTIALSSECRETKEYKEY
OBJECTSTORECONFIG_ACCESSKEY
OBJECTSTORECONFIG_SECRETACCESSKEY

OBJECTSTORECONFIG_ACCESSKEY and OBJECTSTORECONFIG_SECRETACCESSKEY will already exist, point the secret refs to custom-script, update the remaining env vars accordingly, restart server pod, should just work.