Additional updates to PAT buffered expiration flow

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What does this MR do and why?

Fix the placeholder text for the maximum length of the PAT token in the documentation string for the EE feature that sets the maximum allowable days for a token.

Add in a "max" attribute that limits the value here to the maximum value controlled by the buffer_token_expiration_limit.

Introduce a class method for the checking of the timeout and consolidate the other places where this check is used to use this class method.

See issue: #508151 (closed)

EE: true Changelog: fixed

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