Epic: Discontinue student plans for Gitpod and the GitHub marketplace integration

[jldec]

The GitHub student plans and the Marketplace integrations are complex to maintain and support.
Gitpod caters to students with generous Free and Personal plans.

Phase 1 - disable new user signups and upgrades

• Share thinking with community
• Remove student plan pricing from the website.
• Disable new signups and upgrades of student plans via GitHub
• gitpod-io/website#3099
• Disable new student plan signups through the dashboard
• Disable new signups and upgrades through the GitHub marketplace #15570

Phase 2 - migrate users with existing plans tied to GitHub student pack or marketplace

• handled as part of https://github.com/gitpod-io/ops/issues/8319

Related to #6673

For more details and references see RFC (internal).

[jldec]

Example of incorrect Gitpod plan names in GitHub marketplace from support (internal) - user clicked on upgrade in Gitpod. The "Professional" plan in Github is out of date. This plan is now called "Unleashed" and has different features.

[geropl]

Done, last bits superseeded by https://github.com/gitpod-io/ops/issues/8319