Move Getting Started guides + reorganize menu

[erikaheidi]

What should this PR do?

This PR:

• Moves "Getting Started" image guides to their own section under "Chainguard Images", something we need to do in order to change the image reference pages to use tabs.
• Moves "Registry" section to the top-level "Chainguard Products" menu
• Reorganizes menu for better readability and easy access to content
• Adds redirects to "registry" section and individual tutorials that were relocated
• Adds a missing redirect to the "Network requirements" section that has been recently moved

Preview: https://deploy-preview-993--ornate-narwhal-088216.netlify.app/chainguard/chainguard-images/getting-started/getting-started-postgres/

This is how the new menu should look like after the changes:

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[ltagliaferri]

Thanks, Erika! I don't think you need to do this in this PR, but what do you think if we changed the linkTitle to be the name of the image rather than the whole long "Getting Started with ...." title?

[erikaheidi]

Thanks, Erika! I don't think you need to do this in this PR, but what do you think if we changed the linkTitle to be the name of the image rather than the whole long "Getting Started with ...." title?

That makes sense! I was unsure about this one. Let me do it now already :)

[erikaheidi]

Updated, It's much better now!