#8026229 `/read/subscriptions`: Render `SiteSubscriptionsManager` component

Before	After

Fixes #77541
Fixes #77636

Proposed Changes

• We’ve developed the SiteSubscriptionsManagerContext to streamline the storage of several key values related to user interactivity. These include searchTerm, handleSearch, sortTerm, setSortTerm, filterOption, setFilterOption, and siteSubscriptionsQueryResult.
  • The purpose of this context is to encapsulate the complexities tied to functionalities like searching, sorting, filtering, and querying. This not only simplifies the usage of the SiteSubscriptionsManager component when reused, but also retains flexibility in determining the sequence and composition of child components.
• Several small style adjustments were necessary to allow this component to be used outside the new subscriptions’ manager. This was due to some of its styles being applied in stylesheets of its parent components in the previous structure.
• The error message displayed when fetching the site subscriptions fails has been updated to: “Oops! We had a small hiccup with your subscriptions. Could you please try reloading? Thank you!”
• Other cleanup actions include:
  • Removal of the now redundant feature flag subscription-management/sites-list-controlssubscription-management/sites-list-controls.
  • Corrections to class names that did not follow the repo’s guidelines and were impacted by this PR.

Testing Instructions

• Go to http://calypso.localhost:3000/read/subscriptions

• Ensure that:

  • All subscribed-to sites are there
  • Search is functional
  • Sorting is functional

• Go to http://calypso.localhost:3000/subscriptions/sites

• Ensure no visible regressions (you may try other tabs too, i.e. Comments, Pending, Settings)

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests 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-ajp-p2)?