box.ctl: rename clear_synchro_queue to promote

New function name will be `box.ctl.promote()`. It's much shorter and
closer to the function's now enriched functionality.

Old name `box.ctl.clear_synchro_queue()` remains in Lua for the sake of
backward compatibility.

Follow-up #5445
Closes #3055

@TarantoolBot document
Title: deprecate `box.ctl.clear_synchro_queue()` in favor of `box.ctl.promote()`

Replace all the mentions of `box.ctl.clear_synchro_queue()` with
`box.ctl.promote()` and add a note that `box.ctl.clear_synchro_queue()`
is a deprecated alias to `box.ctl.promote()`