AzureAISearchTool: Filter should not be defined at the agent level

For [Azure AI Search Tool](https://learn.microsoft.com/en-us/azure/ai-foundry/agents/how-to/tools/ai-search?view=foundry&tabs=keys%2Cazurecli&pivots=python), `filter` is defined at the agent level. As per the documentation, filter applies to all queries the agent makes to the index. As a result, if an application has multiple filters, it needs to maintain multiple agents. New filters would require newer agent instances (This could be a maintenance nightmare since each agent can have multiple version).

Azure AI Search tool is being considered as one of the alternatives to On-Your-Data. But, there, filter string can be generated dynamically and can be passed as a string while making chat.completions.create calls.

Considering

cc: @xiangyan99, @guygregory