Account Settings: add a Marketplace Authorizations entry

Users ask why "Marketplace Authorizations" isn't in the Settings panel. The sites Account Settings sidebar (`src/components/account/AccountSidebar/AccountSidebar.tsx:48-50`: wallets/notifications/credits, plus security/delete) has no authorizations entry; the feature lives only in the marketplace app at `/marketplace/settings`, and the navbar presents the two as sibling external entries (`src/components/LandingNavbar/navbarConfig.ts:70-72`), which reads as arbitrary.

Recommended: add an "Authorizations" item to the AccountSidebar linking to `https://decentraland.org/marketplace/settings` — small and low-risk. Porting the page itself was assessed and rejected for now: it's Redux + connected-Web3 + per-contract lookups (`CREDITS_MANAGER`, `COLLECTION_STORE`), effectively a rewrite, and the auth models differ (localStorage identity vs web3 provider).