Reset registration.

[pixlwave]

This PR makes 2 changes to the authentication.

• Always load the default homeserver (or provisioned one) when starting a new auth flow
• If an error occurs when starting a new auth flow, show the server selection screen instead of an error (so the user can potentially choose a different server to fix the error).

Fixes #6489.

[sonarcloud]

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[github-actions]

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