Add Zendesk macros for Linux Foundation members flow

Why is this change being made?

We are working with the Linux Foundation (LF) to make it easier for their member projects to apply to the GitLab for Open Source program.

LF members will need to sign the same negotiated terms that the Linux Foundation did. Right now, the only way to do this is for the OSS application processing team to generate a quote, submit a legal request to modify the order form on the quote, and then send the quote to the LF member for signature.

This MR adds a Zendesk template to the handbook to make it easier to request legal's help in modifying the quote. I've already added the macro on Zendesk.

Useful links:

• Relevant issue about negotiated terms for LF members: https://gitlab.com/gitlab-com/legal-and-compliance/-/issues/464#note_550521347
• Partnership issue with LF: https://gitlab.com/gitlab-com/marketing/community-relations/opensource-program/linux-foundation/-/issues/5 (public issue) https://gitlab.com/gitlab-com/marketing/community-relations/opensource-program/general/-/issues/216 (internal issue)

Author Checklist

• 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 one of the people listed in the "Maintained by" section in on the page being edited.
  • 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. (this requirement has been removed pending identification of a new DRI for the handbook)