Add information about when FSA rollover funds are available

Why is this change being made?

HB doesn't mention when rollover amounts are unavailable for current year expenses, nor does WEX Benefits website. Had to get this information via a call to WEX Benefits. WEX Benefits attempts to alarm you with email notices of expiration of funds, but funds under the limit will rollover (just takes time to appear).

Example email from WEX (that makes no mention of rollover funds):

Subject: Your WEX Final Filing Date and Remaining Balance Reminder Date: 2023-03-02 Text: The final filing date for your WEX account is coming up and you have an available balance. All claims must be filed by the deadline to be eligible for reimbursement. You can locate your final filing date and file claims in your online account at benefitslogin.wexhealth.com.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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