docs: refactor zkstack docs

[sarahschwartz]

• Renames ZKsync Stack back to ZK Stack
• Refactors ZK Stack docs for ZKsync OS
  • Reorders/renames sections
  • Moves Airbender docs from protocol to ZK Stack
  • Moves "Launch your chain" buttons up to default/first options on landing page
  • Adds ZKsync OS and ZKsync OS Server pages to chain components
  • Separates customizations from basics of running a chain
  • Moves CTM addresses to protocol
• Updates key features on ZKsync chains page

TODO:

• Confirm if era-fee-withdrawer repo will still be used
• New link redirects
• Confirm latest RaaS providers

What isn't updated:

• zkstack quickstart
• Proving setup instructions (need to confirm if prover command will be updated to use airbender, new system requirements
• Prividium docs (this will happen in other PRs)
• Instructions for L2 tx filtering

[github-actions]

Visit the preview URL for this PR (updated for commit 8d58941):

https://zksync-docs-staging-5eb09--pr446-zk-stack-94cfsg67.web.app

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