Add support for adding named parameters using dictionaries.

[elexisvenator]

New methods:

void ICommandBuilder.AddParameters(IDictionary<string, object?> parameters);
void ICommandBuilder.AddParameters<T>(IDictionary<string, T> parameters);

These will take the passed in dictionary and parse it as a set of named parameters. Additionally, ICommandBuilder.AddParameters(object) will now detect if the passed in object is an IDictionary with a key type of string, and if so will pass to the new methods to handle.

This does result in a change of behaviour for the existing AddParameters method, but the old behaviour when passing a dictionary in would have been for npgsql to throw an error, so not seeing this as a downside.

Testing - added/updated tests to cover both the new methods and new behaviour in existing methods (in both the command builder and batch builder)

Next steps: update marten to support this, document named params in marten (both via anon objects and via dictionaries)

[jeremydmiller]

@elexisvenator I'll process this one today. CI stopped working with Weasel and we don't understand why yet. Tests are behaving perfectly hunky dory locally, and Marten/Wolverine as well.