Improve serverless handling and AzureAISearchSource as input

[jingyizhu99]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

Sample notebook updated accordingly: https://github.com/microsoft/promptflow/blob/9de72467d945112ec1e91ab323e61a6658333ead/src/promptflow-rag/build_index_sample.ipynb

All Promptflow Contribution checklist:

• The pull request does not introduce [breaking changes].
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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Testing Guidelines

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