Installer should detect existing NodeJS runtime

[ppawlowski]

Description

The Device Agent installer should detect if there is already NodeJS runtime environment available on the system. Once detecteted, it should compare the versions and ask user for a decision which one should be used for the installation.
If the version is lower than we exepect, installer should print a warning. Also, we should consider installing different version of the Device Agent.

Customer Value

Having multiple versions of NodeJS on your machine can get very messy very quickly, causing headaches for customers already with NodeJS installed. The recommended install route with the installer also assumes no NodeJS is present, which in a lot of cases won't be appropriate, this will cover that use case.

This is also relevant for #488 where the Opto 22 devices have limited storage, but already have NodeJS installed, us not installing NodeJS will prevent https://flowfuse.com/docs/device-agent/install/device-agent-installer/#error%3A-disk-space-check-failed occurring

Epic/Story

No response

[joepavitt]

Please so make sure that we are recording customer-value in these issues too. I've added a "Customer Value" section to the issue, please correct if I've missed something

Is the sizing of 3-days of work still appropriate here?