Implement remote admin action: Update receipt mode

[smatting]

This PR is the first in a series of PR that add missing implemention of conversation actions when the admin is remote (i.e. the admin is on a backend that doesn't own the conversation).

This PR implements functionality for the receipt mode update in the Client API

PUT /conversations/:domain/:conversation/receipt-mode

when :domain is a domain that is remote to the user calling the endpoint.

This PR also introduces a Federation API RPC update-conversation which is used by a backend to request a conversation update on the backend that owns the conversation. The requested action is any one of the supported conversation actions:

• ConversationJoin
• ConversationLeave
• ConversationRemoveMembers
• ConversationMemberUpdate
• ConversationDelete
• ConversationRename
• ConversationMessageTimerUpdate
• ConversationReceiptModeUpdate (gets used by /conversations/:domain/:conversation/receipt-mode)
• ConversationAccessData

Checklist

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