chore: Dockerfile - Add SHELL instruction

[polarathene]

Related:

• chore: Dockerfile - Add SHELL instruction mistral.rs#1612 (motivation for addition)
• Dockerfile: catch errors at every step #238 (comment) (request to add)

Closes: #238

[polarathene]

@guoqingbao you should not have accepted #279

This PR is a far better solution that better addresses the concern raised.

The related OneAPI repo addition they contributed in the past already had issues that were addressed here

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That author is known to be incompetent with their contributions to Dockerfile.

• I have frequently explained to them when they have misunderstandings (with verbose proof) that they choose to ignore.
• After ignoring my feedback, they sneak their changes in through another PR attempt.

The first instance I noticed this subversive behaviour with PRs was their original Dockerfile contribution to candle-vllm (despite receiving earlier feedback blocking a similar PR of theirs for mistral.rs).

We've already reverted some changes they snuck passed review before. #279 was effectively changes plucked from #238 (despite the author being informed their solution was not appropriate).