WIP: Implement new Contribution Agreement process to support Series LLC change

[krook]

New CNCF projects will use the digital Contribution Agreement document to transfer their project to the CNCF as part of onboarding. This supports the new approach of establishing new projects in their own Series LLC (details, GB resolution, GB vote) and replaces the previous process that focused solely on trademark assignments.

CNCF staff need to update various documents to support this change for projects now onboarding that have not yet completed a trademark assignment form and for those new projects that will onboard in 2025.

• Update the application GitHub issue template to include information on the contributing organization contact info.
• Update the onboarding GitHub issue template that's mostly used by projects voted into the Sandbox. This also includes some projects that come in as Incubating projects.
• Update open onboarding issues that have not yet completed a trademark assignment to reflect the template change and new document.
• Archive the older trademark assignment PDFs.
• Update guidance on what should be in website footers.

Existing projects that have completed a trademark assignment in the past will be converted to a Series LLC model in phases in 2025. Work will be tracked separately for that work.

Related: #894