Switch to microsoft/mssqldb package

[dmathieu]

The denisenkom/go-mssqldb explicitly says in its readme:

For more recent updates, see the Microsoft fork.

So this PR switches our use of that module for the official one from Microsoft.

[kruskall]

I think we should either support the old prefix or drop support for the old repo and release a new minor version (e.g. 2.5.0 ?)

[dmathieu]

Supporting the old prefix is tricky, as the only way we could do it is with two different driver names, which would be strange, as folks not using our instrumentation will not use the name we set here.
So I think releasing a minor version is what we need here.

[v1v]

run docs-build

[thibleroy]

Hello guys, thank you for the switch to microsoft package!
There might be an issue btw, I am not able to perform a SELECT Id FROM Table WHERE Id = $1 ; I get a no rows returned from row.Scan.
Actually I am able to retrieve rows using the formatted query:

// NOK
	query := "SELECT Id FROM Customer WHERE Id = $1"
	var customer Customer
	row := db.QueryRowContext(apm.ContextWithTransaction(context.Background(), tx), query, 2)
// OK
	query := fmt.Sprintf("SELECT Id FROM Customer WHERE Id = %d", 2)
	var customer Customer
	row := db.QueryRowContext(apm.ContextWithTransaction(context.Background(), tx), query)

Here is how I init my db instance:

package main

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"os"

	"github.com/sirupsen/logrus"
	"go.elastic.co/apm/module/apmsql/v2"
	_ "go.elastic.co/apm/module/apmsql/v2/sqlserver"
	"go.elastic.co/apm/v2"
)

func main() {
	settings, err := LoadSettings("server.conf.json")
	dsn := settings.Database.String("go-test")
	db, err := apmsql.Open("sqlserver", dsn)
	if err != nil {
		logrus.StandardLogger().Fatal(err)
	}
	defer db.Close()

[thibleroy]

We should update the documentation to add the sqlserver option in the driver list