Add cookie test to login page

[DL6ER]

By submitting this pull request, I confirm the following (please check boxes, eg [X] - no spaces) Failure to fill the template will close your PR:

Please submit all pull requests against the development branch. Failure to do so will delay or deny your request

• I have read and understood the contributors guide.
• I have checked that another pull request for this purpose does not exist.
• I have considered, and confirmed that this submission will be valuable to others.
• I accept that this submission may not be used, and the pull request closed at the will of the maintainer.
• I give this submission freely, and claim no ownership to its content.

How familiar are you with the codebase?: 10

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Show notice if cookies are disabled on the login page (the login token cannot be stored in this case, forcing the user to re-login on every page).

If cookies are enabled: Nothing changes.

If cookies are disabled/blocked: Show info.

Note that this code is aware that the host name might not be pi.hole:

This template was created based on the work of udemy-dl.

[AzureMarker]

Approved