Implement `DbDataSource` support

[lauxjpn]

I really hope to get to building DbDataSource support into EF itself for 9.0; I've added DbDataSource specifically to EFCore.PG in the meantime, so you could copy that, but ideally this would all be managed in the core.

#1813 (comment)

[bgrainger]

Related issue in Npgsql: npgsql/efcore.pg#2400

In dotnet/aspire#1161 (which you may want to review @lauxjpn), I'm having to work around the inability to use MySqlDataSource from DI.