EDU-3275: New pricing structures and legacy overlap

[fairlydurable]

Primary SME/Source of truth: Tomas Lorinc

Notes:

• Blocked on release
• Moved Nexus pricing into place with other pricing since it is "how to count actions"
• Since support was removed, links mentioning support were moved to [Support](/cloud/support#support)
• "Temporal Cloud Plan" is intentionally uppercased.

In November:

• The current pricing is in the file named legacy-pricing.mdx, and is currently called Pricing, slug pricing
• The new pricing is in the file named pricing.mdx, and is currently called Future pricing, slug future-pricing
• sidebars.js updates by adding future-pricing after pricing

In January:

• In January, the slug for pricing.mdx updates to pricing, and the sidebar/title Pricing.
• In January, the slug for legacy-pricing.mdx updates to legacy-pricing, and the sidebar/title Legacy pricing.
• In January, the second slug (future-pricing) is updated to legacy-pricing.
• In January, the texts in the admonition/callouts at the start of the two files are updated to reflect the current state, and inform existing customers that they are still using the previous pricing schedule.

The file names are already prepared for this change.

In February

In February, existing customers will be adopted into the new pricing. At that time:

• Delete the legacy-pricing file.
• Remove the opening admonition/callout from pricing.mdx
• Update sidebars.js and remove the legacy-pricing slug, leaving /pricing in-place.