Use smoldot's database system in the extension

[tomaka]

The extension should periodically call smoldotClient.databaseContent() for the hardcoded chains (Polkadot, Kusama, Rococo, Westend) and save the result in local storage.
When the extension is loaded, it should load the local storage and pass the content to the configuration passed to addChain.

Smoldot will not return any error if a bad database content is passed, so there's no need to worry about this.

[tomaka]

Since smoldot 0.5.8 there's an optional parameter for databaseContent to provide the maximum size of the database.