Update push token on login to allow multiple users on mobile devices

[trmartin4]

https://bitwarden.atlassian.net/browse/SG-816
https://bitwarden.atlassian.net/browse/SG-814
https://bitwarden.atlassian.net/browse/SG-823

Type of change

- [X] Bug fix
- [ ] New feature development
- [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
- [ ] Build/deploy pipeline (DevOps)
- [ ] Other

Objective

We are experiencing a problem today where push notifications are not being sent to mobile devices when there are multiple users logged in.

There is still a scenario where no push token would get set for a given user + device combination, and that would be if a user logs in to a device and gets an access token prior to the PNS providing a push token to the device. However, if such a scenario occurs, the user can log out and log back in with that user and the token would be updated on the subsequent authentication request.

Code changes

BaseRequestValidator.cs:

• When request for a token comes to Identity, we used to only call CreateOrUpdateRegistrationAsync() (as a part of SaveAsync() on the DeviceService) when it was a new device. This meant that subsequent login requests never updated the push token.
• I changed this so regardless of whether the device is new or existing, every login request will attempt to set the push token for that logged-in user in the Azure Notification Hub.

AuthRequestsController:

• Added userId to lookup for the correct device, in case there are multiple logged in

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