UI configuration

[dogmatic69]

Objective

• allow configuration from UI
• remove yaml config for simplicity in the code

Possible flow

Once off

• enter secret id / key (no point having multiple with the way nordigen is setup, all keys have the same data. Possibly multiple nordigen accounts, but less likely)

Multiple

This can be done any number of times

1. Pick a country
2. If not already done, set's up country sensor for institution tracking
3. Pick an institution
4. Pick a user the account belongs to
5. setup requisition (when not linked should start with high update frequency
6. provide link for user to authenticate
7. Wait for link to be detected (polling)
8. List accounts to track / ignore
9. Option for currency conversion (linked currency sensor)
10. save

Add the config flow stuff to allow config via UI rather than yaml.

[dogmatic69]

Could be a good first issue for someone that knows HA config flow system (I sure don't 😂)