Launch Day | OSS Marketing Page Form SheerID - June 8, 2021

Why is this change being made?

This MR updates the what to expect section of the OSS join page and swaps out the existing Marketo application form for the new SheerID application.

These changes are part of the Community Efficiency Interim Launch Plan.

This MR aims to make most of the same changes as the EDU form launch day update.

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)