[Rust APIView] SecretClient constructor guideline references outdated AsRef parameter guidance

Bad code snippet:
```Rust
pub fn new(endpoint: &str, credential: Arc<(dyn TokenCredential)>, options: Option) -> Result {}
```

What it should do:
The APIView comment cites the Rust `AsRef` parameter guideline and suggests changing `endpoint` to `impl AsRef`, but that guideline is out of date and the referenced `#rust-parameters-asref` section no longer exists. The documentation/guideline should be updated rather than treating this as a current API requirement.

Good code snippet:
```Rust
pub fn new(endpoint: &str, credential: Arc, options: Option) -> Result {}
```

Locate the Rust APIView guideline text that cites the AsRef parameter guidance and the missing #rust-parameters-asref section. Update the documentation so this constructor is not treated as requiring impl AsRef, and confirm the outdated reference is removed or replaced with current guidance.

Written by the indexing model from the issue text.