[DOC] Introduction of derived source feature

[tanik98]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request.
We are introducing a new feature of derived source, which re-generate the source at time of retrieval instead of explicitly storing it on the disk. It will help in reducing the storage requirement.

For now we will be introducing documentation under _source metadata field with supported field types under this feature, later we would extensively introduce feature detail under each of the supported field types.

Version: 3.2.0

What other resources are available?
#9568

[kolchfa-aws]

@tanik98 Is this on track for 3.1?

[tanik98]

@tanik98 Is this on track for 3.1?

Updated the traget version.