ui: move TimezoneProvider to be inside RequiredLogin

Fixes a bug where the login page was making a request for
cluster settings in order to create the timezone provider
context. This request results in a 401 unauthorized since
users need to be authorized to request cluster setting
data. In version before 26.3, this bug made it impossible
to login as a non default tenant via OIDC login, since
this unauthorized response caused tenant cookies to
be cleared before user could click the OIDC button.

Epic: None
Release note: None

Author: kyle-a-wong