Introduce a new MigrateAsync that works with asp.net DI

MigrateAsync currently does 2 things

1. Find classes that implement IMigration
2. Execute the migration logic

We can create a new overload for MigrateAsync that takes an IEnumerable<IMigration> as a parameter, and only executes the migration logic e.g.

public static async Task MigrateAsync(IEnumerable<IMigration> migrationsEnumerable)
{
    var lastMigNum = (
        await DB.Find<Migration, int>()
              .Sort(m => m.Number, Order.Descending)
              .Limit(1)
              .Project(m => m.Number)
              .ExecuteAsync()
              .ConfigureAwait(false))
        .SingleOrDefault();

    var migrations = new SortedDictionary<int, IMigration>();

    foreach (var migration in migrationsEnumerable)
    {
        var t = migration.GetType();
        var success = int.TryParse(t.Name.Split('_')[1], out int migNum);

        if (!success)
            throw new InvalidOperationException("Failed to parse migration number from the class name. Make sure to name the migration classes like: _001_some_migration_name.cs");

        if (migNum > lastMigNum)
            migrations.Add(migNum, migration);
    }

    var sw = new Stopwatch();

    foreach (var migration in migrations)
    {
        sw.Start();
        await migration.Value.UpgradeAsync().ConfigureAwait(false);
        var mig = new Migration
        {
            Number = migration.Key,
            Name = migration.Value.GetType().Name,
            TimeTakenSeconds = sw.Elapsed.TotalSeconds
        };
        await DB.SaveAsync(mig).ConfigureAwait(false);
        sw.Stop();
        sw.Reset();
    }
}

This will allow more control over how to migrate the database

[dj-nitehawk]

oh and when doing the PR, please add test to the tests project pls.

[dj-nitehawk]

added to v20.18.0-beta1