[Feature]: AzureAISearchContextProvider lacks a way to set KnowledgeSourceParams

### Description

KnowledgeSourceParams are crucial to configure AI Search with respect to the retrieval of extra fields (IncludeReferenceSourceData field) and many other advanced behaviours.

### Code Sample

```markdown
Add knowledgeSourceParams in the constructor of AzureAISearchContextProvider:

scc = AzureAISearchContextProvider(..., knowledgeSourceParams=[ ... ])

var scc = new AzureAISearchContextProvider(..., knowledgeSourceParams: [ ... ]);
```

### Language/SDK

Both

Start at the AzureAISearchContextProvider entry points in the Python and .NET SDKs and inspect how their constructors expose other retrieval options. Add support for passing KnowledgeSourceParams in both language variants, then verify the provider behavior with the relevant existing tests; the issue does not name specific files or tests.

Written by the indexing model from the issue text.