chore: add y-indexeddb source to npm

[MentalGear]

Great that you provide the y-indexeddb package, but do add the source on npm (many people are hesitant installing something that does not have a source link).
npm site: https://www.npmjs.com/package/@toeverything/y-indexeddb
source: https://github.com/toeverything/AFFiNE/tree/canary/packages/common/y-indexeddb

[MentalGear]

Also, the readme needs an update as the indicted 'whenSynced' is not available anymore.
Property 'whenSynced' does not exist on type 'IndexedDBProvider'.ts