[Cherry-Pick] s3 storage initializer: only set environment variables if variables are set in storage secret json

[Jooho]

This is cherry-pick of kserve#3259

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Type of changes
Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Feature/Issue validation/testing:

Please describe the tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

• Test A

Test Step:

1. install opendatahub operator and kserve
2. The detail guide is here: https://docs.google.com/document/d/1pf0x1geayFr-06lAQKr96ynVsnOCcpgmAfbgoHgg8AI/edit

Scale down odh operator pod

oc scale deploy/opendatahub-operator-controller-manager -n openshift-operators --replicas=0

Update storage initializer image and restart kserve controler

oc edit cm inferenceservice-config -o yaml -n opendatahub
....
 storageInitializer: |-
    {
        "image" : "quay.io/jooholee/kserve-storage-initializer:ssl-verify",
...

oc delete pod -l control-plane=kserve-controller-manager --force 

3. deploy test isvc(model) in aws https s3 (I used QE team s3 @bdattoma)

Check point
Check the log of init-container "storage-initializer". If the log looks like the following, it works fine

oc logs deploy/caikit-example-isvc-predictor-00001-deployment  -c storage-initializer
INFO:root:Initializing, args: src_uri [s3://modelmesh-example-models/llm/models] dest_path[ [/mnt/models]
INFO:root:Copying contents of s3://modelmesh-example-models/llm/models to local
INFO:botocore.credentials:Found credentials in environment variables.
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/config.json to /mnt/models/flan-t5-small-caikit/artifacts/config.json
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/generation_config.json to /mnt/models/flan-t5-small-caikit/artifacts/generation_config.json
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/pytorch_model.bin to /mnt/models/flan-t5-small-caikit/artifacts/pytorch_model.bin
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/special_tokens_map.json to /mnt/models/flan-t5-small-caikit/artifacts/special_tokens_map.json
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/spiece.model to /mnt/models/flan-t5-small-caikit/artifacts/spiece.model
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/tokenizer.json to /mnt/models/flan-t5-small-caikit/artifacts/tokenizer.json
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/artifacts/tokenizer_config.json to /mnt/models/flan-t5-small-caikit/artifacts/tokenizer_config.json
INFO:root:Downloaded object llm/models/flan-t5-small-caikit/config.yml to /mnt/models/flan-t5-small-caikit/config.yml
INFO:root:Successfully copied s3://modelmesh-example-models/llm/models to /mnt/models

• Logs

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Checklist:

• Have you added unit/e2e tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?

Release note:

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Jooho

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[Jooho]

please do not merge this until everything is ready

[Jooho]

another pr will be sent soon