[Doc][Misc] Add explanations for key parameters. (#14679)

### What this PR does / why we need it?

This PR supplements and modifies the tutorials for Qwen3 models
(Qwen3-235B-A22B, Qwen3-30B-A3B, Qwen3-Coder-30B-A3B, and Qwen3-Dense) :
- adds detailed parameter descriptions for performance tuning across
different scenarios (High Throughput, Low Latency, Long Context) ;
- standardizes arguments like `--distributed-executor-backend "mp"`;
- corrects a documentation link for vLLM Serving Arguments
documentation;
- aligns the Table 2 with the deployment optimized for low latency for
Qwen3-235B-A22B model.

### Does this PR introduce _any_ user-facing change?

No, these are documentation-only updates.

### How was this patch tested?

Documentation changes, verified visually.

- vLLM version: v0.27.1
- vLLM main:
https://github.com/vllm-project/vllm/commit/ba07e4a48fc951300d97eb506217dd530583dea3

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Signed-off-by: Chenzhh69 <1473362125@qq.com>
Signed-off-by: Chenzhh69 <1473362125@11.com>
Co-authored-by: Chenzhh69 <1473362125@11.com>