Referendum proposal's metadata (#12568)

* referenda metadata

* todo comment

* remove TODO, update rustdocs

* referenda clear_metadata origin signed or root

* referenda metadata unit tests

* drop schema type for referenda metadata

* remove metadata type

* referenda metadata benches

* note different preimages

* metadata for democracy pallet

* metadata democracy pallet tests and benches

* fix cargo clippy

* update docs

* ".git/.scripts/bench-bot.sh" pallet dev pallet_democracy

* ".git/.scripts/bench-bot.sh" pallet dev pallet_referenda

* Update the doc frame/democracy/src/lib.rs

Co-authored-by: Roman Useinov <roman.useinov@gmail.com>

* Update the doc frame/democracy/src/lib.rs

Co-authored-by: Anthony Alaribe <anthonyalaribe@gmail.com>

* reference instead clone for take

Co-authored-by: Anthony Alaribe <anthonyalaribe@gmail.com>

* error rename BadMetadata to PreimageNotExist

* clear metadata within internal_cancel_referendum fn

* remove redundant clone

* collapse metadata api into one set_metadata method

* fmt

* review fixes

* not request preimage on set_metadata

* rename events and update docs

* ".git/.scripts/commands/bench/bench.sh" pallet dev pallet_democracy

* ".git/.scripts/commands/bench/bench.sh" pallet dev pallet_referenda

* rename reset_metadata to transfer_metadata

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Co-authored-by: command-bot <>
Co-authored-by: Roman Useinov <roman.useinov@gmail.com>
Co-authored-by: Anthony Alaribe <anthonyalaribe@gmail.com>