add tutorial for conversational search (#2075) (#2101)

* add tutorial for conversational search

Signed-off-by: Yaliang Wu <[email protected]>

* add more doc links

Signed-off-by: Yaliang Wu <[email protected]>

* add advanced topics

Signed-off-by: Yaliang Wu <[email protected]>

* add demo of PPLTool

Signed-off-by: Yaliang Wu <[email protected]>

* Apply suggestions from code review

Co-authored-by: kolchfa-aws <[email protected]>
Signed-off-by: Yaliang Wu <[email protected]>

* remvoe unnecessary setting

Signed-off-by: Yaliang Wu <[email protected]>

* use memory/message to keep consistent

Signed-off-by: Yaliang Wu <[email protected]>

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Signed-off-by: Yaliang Wu <[email protected]>
Co-authored-by: kolchfa-aws <[email protected]>
(cherry picked from commit 7ecc695)

Co-authored-by: Yaliang Wu <[email protected]>

Author: opensearch-trigger-bot[bot]