Allow scheduling rule to assign name to activity directive

[bashbash]

abercrom https://jira.jpl.nasa.gov/browse/AERIEQS-443 Moderate It would be useful if a scheduling rule could set the name of activity directives that it schedules. Sometimes activity types with fairly generic names are used for different purposes. This capability would allow the rule to attach a meaningful name based on the scheduling goal.

EDIT(dailis): in addition to the name, https://github.com/NASA-AMMOS/aerie/issues/777 suggests that other mission-specific metadata could be set by the scheduler.