Oxford Instruments Mercury: Additional Functionality for Temperature Ramps

# Feature Description

As an instrument scientist it would be useful to extent the OI Mercury IOC to have functionality for temperature ramps.

## Explanation
The request we have received:

> Two modes would be useful:
>
> 1. Ramp between ‘start’ and ‘finish’ temperatures at a specified ‘rate’
> 2. Ramp between ‘start’ and ‘finish’ temperatures at a specified ‘rate’, suspending the ramp if beam is off
>
> In the former case, the inbuilt Mercury ramp function could be used, sending the ‘finish’ and ‘rate’ to the controller with an appropriate command would be required. In the latter case, IBEX would need to continually send setpoints to the controller to simulate a ramp at the specified ‘rate’ (K/min), suspending this software ramp while beam was off.

If 2 is particularly complex to achieve then I suspect a solution where we provide a script that suspends the ramp when beam is off may be sufficient for this use case, but it should be explored with the original requester.

### Additional Information
Original request received from SC by email (search EC inbox for "Additional functionality for temperature ramps - OI Mercury").

# Acceptance Criteria
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- [ ] the OI Mercury IOC supports temperature ramping

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# How to Review
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_{**To the reviewer: Make sure to [update submodules](https://isiscomputinggroup.github.io/ibex_developers_manual/processes/git_and_github/Git-workflow.html)!**}