sub add fails if the subscription already exists

[Iain-S]

to recreate

• make a new subscription on Azure at 59 minutes past the hour
• run rctab sub add ... 2 minutes later
• you will get an error message

  Failed with status code: 409. Details: {'message': 'One of the records already exists. Details: Key (subscription_id)=(123-456-789-10112) already exists.'}
  
  

We will probably want to catch the "subscription exists" error here and ignore / log it:

https://github.com/alan-turing-institute/rctab-cli/blob/2062874a1f457d822b334d9259a9c4b02c6c9536/rctab_cli/sub_apps/sub.py#L237C1-L237C38

and then carry on with the persistence and allocation steps.

[joseph-palmer]

When I ran sub add on an existing subscription, I got that error message but the approval was then processed correctly. Perhaps a different error message like 'Sub add failed as one of the records already exists. Continuing with approval and allocation' is warranted?