Cleanup Objective files, add PickSpecificPersonComponent (#35802)

* cleanup objectives

* remove unrelated access restriction

* review

Content.Server/Objectives/Components/PickSpecificPersonComponent.cs

@@ -0,0 +1,8 @@
+namespace Content.Server.Objectives.Components;
+
+/// <summary>
+/// Sets this objective's target to the one given in <see cref="TargetOverrideComponent"/>, if the entity has it.
+/// This component needs to be added to objective entity itself.
+/// </summary>
+[RegisterComponent]
+public sealed partial class PickSpecificPersonComponent : Component;