Microsoft.Data.Sqlite: Add Default Timeout connection string keyword

[bricelam]

We should add the Default Timeout connection string keyword. Order of precedence would be:

1. SqliteCommand.CommandTimeout (always wins if set)
2. SqliteConnection.DefaultTimeout
3. Default Time= in the connection string
4. 30 (the ADO.NET default)

[bricelam]

Note to implementor: make sure Command Timeout is also valid since that seems to be the de facto standard.

[roji]

Yeah, Command Timeout is what everyone does. Note that I'm not aware of others providing DbConnection.DefaultTimeout, but that's not a reason not to do it.

[nmichels]

Hi there! I'm trying to implement a solution for that Issue, PR attached. Please let me know if the approach is right. Thanks in advance!