fix: Avoid string concat and regex inefficiency

[rafvasq]

This PR makes the following changes:

• Execute external commands using an array of strings rather than a single string as per https://github.com/kserve/modelmesh/security/code-scanning/2
• Make the regular expression pattern a bit more efficient
  https://github.com/kserve/modelmesh/security/code-scanning/1

[njhill]

Thanks @rafvasq. Performance is not important in these contexts (readability should be the main thing). But the changes are fine with me if they suppress the warnings.

[ckadner]

Thanks @rafvasq

/lgtm

[kserve-oss-bot]

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This pull-request has been approved by: ckadner, njhill, rafvasq

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