Update the GitLab address in community/sweepstakes/ and CA Merchandise Handbook
As per note in the #community-relations channel:
- I've removed the old GitLab address from the Community Advocate Merchandise request workflow handbook section.
- I've updated the GitLab Address in community/sweepstakes pages.
Also, I've made changes and added more details on how the GitLabbers should request the merchandise and how the Community Advocates should fulfill those requests in the CA Merchandise handbook.