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

[Woody1193]

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.

[diegommm]

Hi @Woody1193! Thank you very much for your contribution :heart: