settings: Update label for realm-level default of send_read_receipts.
settings: Update label for realm-level default of send_read_receipts.

zulip/zulip,andersk/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,rht/zulip,rht/zulip,andersk/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip