user docs: Move "Create a poll" section in Sending messages.
user docs: Move "Create a poll" section in Sending messages.

Fixes #18312.

eeshangarg/zulip,zulip/zulip,hackerkid/zulip,eeshangarg/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,andersk/zulip,kou/zulip,zulip/zulip,kou/zulip,kou/zulip,zulip/zulip,punchagan/zulip,andersk/zulip,eeshangarg/zulip,hackerkid/zulip,rht/zulip,andersk/zulip,andersk/zulip,kou/zulip,zulip/zulip,rht/zulip,rht/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,eeshangarg/zulip,punchagan/zulip,punchagan/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,kou/zulip