refactor: Allow custom msg strs in send_message_moved_breadcrumbs.
refactor: Allow custom msg strs in send_message_moved_breadcrumbs.

This is a prep commit which modifies the
`send_message_moved_breadcrumbs` function to take
message strings as input.
This is done to reuse the function in other places
like the /digress command.

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