Momentary signals mechanism

Is there a mechanism for momentary signals in dodal?

Currently synoptic buttons that send a value when pressed and another value when released to momentarily set the value of an ioc's PV. For example on the pressure cell valve OPEN_SEQ pvs e.g. BL38P-EA-HPXC-01:V1:OPENSEQ. For the pressure jump cell case a delay using `asyncio.sleep` was used but this kind of signal could be standardised in dodal.

Orginally came up in - https://github.com/DiamondLightSource/dodal/pull/812#discussion_r1787716082