chore(plg): provide user Cody plan on a route level

[taras-yemets]

1. Lifts the user Cody plan query to Sourcegraph GraphQL backend up to the route level.

All Cody Pro pages require the user’s Cody Pro plan to determine their behavior. Previously, we had repetitive logic to fetch this data and handle loading and error states. This PR moves the fetching of the user’s Cody plan to a higher level, simplifying the code. Now, each Cody Pro page component receives the subscription data as a prop.

2. Creates a Custom Hook for Fetching the User’s Cody Plan.

3. Refactors "/cody/subscription" page component.

• Updates the CodySubscriptionPage component to use the withAuthenticatedUser higher-order component. This change removes the need for an authenticated user check within the component itself, making it more consistent with other Cody Pro page components.
• Removes redundant isCodyEnabled() check.
  • "/cody/subscription" route is only rendered on dotcom and if the Cody feature is enabled in the license.
  • The isCodyEnabled() check consists of two fields from jscontext:
    • codyEnabled: reads its value from the site config and it's obviously true for dotcom
    • codyEnabledForCurrentUser: returns false only if the actor is not authenticated, which is already ensured at a higher level (see 2.).

Test plan

• CI
• Run Sourcegraph in dotcom mode locally and compare the authenticated user related logic with sourcegraph.com

[vdavid]

Nice! Thanks for the refactor, so much nicer now.

Note: I think you forgot to finish or remove the "Changelog" section.

[vdavid]

Hmm, I wonder if we can do better, and redirect the user back to the page they wanted to view, including the query params. Would be a lot helpful to users.
Could be out of scope for this PR, but if so, it'd be great to track this as a new gap.