feat: Add goose provider

[mfridman]

Fix #379.

This PR ports all the provider code from ./internal/provider to package goose. I'll write a blog post or two about the provider features. Briefly, all functionality is now scoped to a *goose.Provider, which enables folks to have multiple *goose.Provider in the same runtime.

The default path should be easy for most users.

• pick your sql driver (e.g., _ "modernc.org/sqlite")
• match the dialect (e.g., database.DialectSQLite3)
• supply a filesystem (e.g., os.DirFS("path/to/migrations"))
  • or register Go migrations with goose.WithGoMigrations
  • or both!

And then run methods on the provider, e.g., results, err := provider.Up(ctx)

Simple example

// Create a sqlite database for testing.
db, err := sql.Open("sqlite", ":memory:")
check.NoError(t, err)
// Create a new goose provider.
provider, err := goose.NewProvider(
	database.DialectSQLite3,
	db,
	os.DirFS("testdata/migrations"),
)
check.NoError(t, err)
// Apply all "pending" migrations.
results, err := provider.Up(context.Background())
check.NoError(t, err)
for _, r := range results {
	fmt.Printf("OK  %s  %s %s\n", truncateDuration(r.Duration), r.Source.Type, r.Source.Path)
}

OK  1.68ms  sql 00001_users_table.sql
OK  1.25ms  sql 00002_posts_table.sql
OK  1.17ms  sql 00003_comments_table.sql
OK  1.03ms  sql 00004_insert_data.sql
OK  1.29ms  sql 00005_posts_view.sql