[lib] Introduce `messageStoreOperation` for `updateMultimediaMessageMediaActionType` in `reduceMessageStore`
[lib] Introduce `messageStoreOperation` for `updateMultimediaMessageMediaActionType` in `reduceMessageStore`

Summary: last action type to be handled in `reduceMessageStore`

Test Plan: invariant

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: palys-swm, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D1874

Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal