Keep only archived version of previous executions

Currently, the execution vertex stores a limited amount of previous executions in a bounded list. This happens primarily for archiving purposes and to remember previous locations and allocation ids. We remember the whole execution to eventually convert it into an archived execution.
This seems unnecessary and dangerous as we have observed that this strategy is prone to memory leaks in the job manager. With a very high vertex count or parallelism, remembering complete executions can become very memory intensive. Instead I suggest to eagerly transform the executions into the archived version before adding them to the list, i.e. only the archived version is ever still referenced after the execution becomes obsolete. This gives better control over which information about the execution should really be kept in memory.