release-26.2: ui: move TimezoneProvider to be inside RequiredLogin

[kyle-a-wong]

Backport 1/1 commits from #169751 on behalf of @kyle-a-wong.

/cc @cockroachdb/release

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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

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Release justification: Fix for a bug that prevents non-default tenant OIDC login

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate.

[trunk-io]

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[cockroach-teamcity]

This change is 

[kyle-a-wong]

Before this PR:
https://www.loom.com/share/6f7bbf3fdbb14bfabe600486959765af
After this PR:
https://www.loom.com/share/f6cde969fc8746c39e228f99c744d0a3