Update sending messages (POST /messages) to support using "direct" as the message type for direct/private messages.
Auto-translate "direct" to "private" for servers that it knows via the the Client initialization check on the API feature level don't support it; "direct" was introduced at API feature level 174.
As follow-up to https://github.com/zulip/zulip/pull/25154 (which fixed https://github.com/zulip/zulip/issues/24960), we should:
POST /messages) to support using "direct" as the messagetypefor direct/private messages.Clientinitialization check on the API feature level don't support it; "direct" was introduced at API feature level 174.See #api design > message type parameter, #24960 for relevant context and discussion.