Don't Fall Over if a Device Does not Connect

[callumforrester]

As a user I would still like to use blueapi if a particular device fails to connect, assuming there are still plans available that can be used without it, so I can continue operations even if a PV is wrong or a device is unavailable.

This is relevant to, but distinct from #440. If this issue is implemented we expect blueapi to start even if a device does not connect but fall over if we try to use it. Implementing #440 would mean it gives a sensible error if we try to use it.

Implementing this behaviour would also be inkeeping with #285. Blueapi's design philosophy seems to be evolving towards: "start even if there's nothing you can use, and report it".

Possible Solution

Currently unsure if the code change required is in blueapi or dodal

Acceptance Criteria

• If an error occurs instantiating or connecting to a device, blueapi still starts up
• In this circumstance, the devices that did successfully instantiate or connect are still available in blueapi
• There are tests that prove this

[callumforrester]

This shouldn't have been closed with #468 still open