Add Table of Contents and footer link to Finance Expenses page

Why is this change being made?

Add Table of Contents and footer link to Finance Expenses page

Appears that some content previously housed at handbook/spending-company-money was ported to /handbook/finance/expenses with no breadcrumb or cross-link from the prior page to the new page. This merge request attempts to remedy this.

Note that handbook/spending-company-money and /handbook/finance/expenses have some amount of duplicate content at the moment, including sub-headers for Expense Policy, Advance, and Approving Expense Report. I didn't attempt to remove one or the other as I'm unsure which Finance wants to treat as the single source of truth.

Author Checklist

• Correct MR template applied (e.g blog post)
• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.

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