Evaluate VPAT against GitLab v15.0

Purpose

In Evaluate VPAT against GitLab v14.0 (#1032 - closed) the team evaluated against 14.0 and created the VPAT WCAG report, currently available for everyone to view. As we move towards 15.0, US Public Sector prospects and customers will require an updated version of the VPAT or a statement that states "no material difference from 14.0" if there are no differences from that version. The general timing for the prospect to ask for VPAT is either during procurement (which can be any time of the year) or when existing customers plan to upgrade to the latest version which would likely be as soon as 15.0 is released.