Document how to use Gorm with Cloud SQL Go Connector

[enocom]

Currently the Gorm docs showcase how to connect to Cloud SQL using the v1 Cloud SQL Proxy. Meanwhile, there is a newer Cloud SQL Go Connector.

This is a request to update the docs to show how to use the Cloud SQL Go Connector with Gorm.

If there's interest, I'm happy to send the PR to do this work. Opening an issue to discuss first.

Here's a full example:

package main

import (
        "fmt"
        "time"

        "cloud.google.com/go/cloudsqlconn"
        "cloud.google.com/go/cloudsqlconn/postgres/pgxv5"
        "gorm.io/driver/postgres"
        "gorm.io/gorm"
)

func main() {
        cleanup, err := pgxv5.RegisterDriver("cloudsql-postgres")
        if err != nil {
                panic(err)
        }
        // cleanup will stop the driver from retrieving ephemeral certificates
        // Don't call cleanup until you're done with your database connections
        defer cleanup()

        dsn := "host=my-project:us-central1:my-instance user=postgres password=postgres dbname=postgres sslmode=disable"

        db, err := gorm.Open(postgres.New(postgres.Config{
                DriverName: "cloudsql-postgres",
                DSN:        dsn,
        }))
        if err != nil {
                panic(err)
        }

        // get the underlying *sql.DB type to verify the connection
        sdb, err := db.DB()
        if err != nil {
                panic(err)
        }

        var t time.Time
        if err := sdb.QueryRow("select now()").Scan(&t); err != nil {
                panic(err)
        }

        fmt.Println(t)
}

cc @jackwotherspoon

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[github-actions]

The issue has been automatically marked as stale as it missing playground pull request link, which is important to help others understand your issue effectively and make sure the issue hasn't been fixed on latest master, checkout https://github.com/go-gorm/playground for details. it will be closed in 30 days if no further activity occurs. if you are asking question, please use the Question template, most likely your question already answered https://github.com/go-gorm/gorm/issues or described in the document https://gorm.io ✨ Search Before Asking ✨