Added SqlMock type to allow for options to be sent to function that creates the sqlmock

[Woody1193]

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This PR addresses an issue where the user wants to embed the SqlMock creation code into a function, like so:

func createServiceMock(database string, schema string, opts ...sqlmock.SqlMockOption) (*MyDB, sqlmock.Sqlmock) {

	db, mock, err := sqlmock.New(opts...)
	Expect(err).ShouldNot(HaveOccurred())

	svc := FromConnection(database, schema, db)

	return svc, mock
}

With the current implementation of go-sqlmock, this cannot done because the option references a type internal to the go-sqlmock package. By adding an alias for this type, the user can now send such options without exposing the internal sqlmock type.