[mgt] Remove LOGIN_SESSION_TIMEOUT from the m Cookie (backport #16894)

[mergify]

Proposed Changes

Remove unnecessary pseudo-cookie (entry stored within the m cookie) .
This change is part of an effort of securing cookies. All cookies that exists in the management ui are now owned by the server and fully secured with the right attributes. The only cookie left is m, controlled by the client side, which only exists for the pseudo-cookie LOGGED_IN which has a TTL that controls the lifespan of the client-side session. This cookie has no value hence it is fine that it is not fully secured because javascript created cookies cannot be fully secured.
Also, this pseudo-cookie needs to be accessed by javascript hence it cannot be owned by the server.

Types of Changes

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• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)
• Build system and/or CI

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This is an automatic backport of pull request #16894 done by [Mergify](https://mergify.com).

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