Makes ImmovableAttribute configurable

[ledjon-behluli]

Following some discussions in discord, its apparent that automatic migration by means of LAR or MAR can be mutually inclusive, even for short periods of time. It appears to be beneficial to allow a grain type to be migrated automatically by the runtime component (LAR, MAR, AA placement (future)) but not allow for others.

This PR adds a an enum ImmovableKind as an optional parameter to ImmovableAttribute

/// <summary>
/// Emphasizes that immovability is restricted to certain components.
/// </summary>
[Flags]
public enum ImmovableKind : byte
{
    /// <summary>
    /// Activations of this grain type will not be migrated by the repartitioner.
    /// </summary>
    Repartitioner = 1,
    /// <summary>
    /// Activations of this grain type will not be migrated by the rebalancer.
    /// </summary>
    Rebalancer = 2,
    /// <summary>
    /// Activations of this grain type will not be migrated by anything.
    /// </summary>
    Any = Repartitioner | Rebalancer
}

Microsoft Reviewers: Open in CodeFlow

[ledjon-behluli]

Note: ActivationRebalancerWorker has [Immovable] applied to it, which translates to [Immovable(Kind = ImmovableKind.Any) as it must not be affected by the repartitioner, nor the rebalancer itself.