#12722465 Domains: Enable NS records editing for subdomains

Proposed Changes

This PR enables adding NS records in Calypso.

NS records can now be added to a domain or subdomain in the DNS management page. If you are adding an NS record to a root domain, you’ll need to provide a name for the record, since the root NS records for a root domain cannot be changed. If you’re adding NS records to a subdomain, the name field is optional since you can update either the subdomain’s root records or a subdomain of the subdomain’s.

Screenshots

• Adding NS records to root domain

• Adding NS records to a mapped subdomain

• If there are no custom NS records in a mapped subdomain, the “Handled by WordPress.com” row should be shown (only when managing the DNS of mapped subdomains)

Testing Instructions

Note: this PR depends on D144574-code, so please apply it to your sandbox

• Open the live Calypso link or build this branch locally
• Go to the domain management page of a root domain
• Go to the DNS management page and try adding, updating and removing NS records
• Ensure you can’t leave the name field empty
• Go to the domain management page of a mapped subdomain
• Go to the DNS management page and try adding, updating and removing NS records
• Try adding NS records with and without the name field

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?