Deprecate LogoutButton

[leeagustin]

Fixes #2894.

PR will output a DeprecationWarning when the LogoutButton is used.

I tried making the changes from https://github.com/plotly/dash/issues/2894#issuecomment-2176661569, but it seems that it only validates the initial page layout and not the components used in callbacks.

As seen in the modified test in this PR, the test doesn't output a DeprecationWarning and fails when the LogoutButton is in the callback but not in the initial page layout. On the other hand, it passes when LogoutButton is in the initial page layout.

I'm assuming we would also want to show a DeprecationWarning if LogoutButton is used in a callback. What would be a good way to approach this? Or would it be simpler to remove the LogoutButton component entirely?

Contributor Checklist

• [x] I have broken down my PR scope into the following TODO tasks
  • [x] Outputs DeprecationWarning if LogoutButton is used in layout
  • [ ] Outputs DeprecationWarning if LogoutButton is used in callback
• [ ] I have run the tests locally and they passed. (refer to testing section in contributing)
• [x] I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• [ ] I have added entry in the CHANGELOG.md
• [ ] If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • [ ] this GitHub #PR number updates the dash docs
  • [ ] here is the show and tell thread in Plotly Dash community