aerie-ui External Event Timeline Filtering

This PR adds external events to the advanced timeline filtering capability (see: https://github.com/NASA-AMMOS/aerie-ui/pull/1535). The filtering capability allows filtering based on external event type and any attributes defined for the events.

The filtering essentially works the same as the aforementioned activity filtering capability by exposing the following filters for external events:

Manually selected/Static external event type(s)
Dynamically selected by external event type(s) name
Dynamically selected by external event name(s)
Dynamically selected by external event attributes

Attribute filtering supports simple and complex types, including nested objects. For example, the filter below accesses a field complex that is nested underneath two other parent objects.

The feature can be accessed through clicking the filter icon/bar inside an 'Events Layer' within the Timeline Editor panel - the same way a user accesses the filtering for activities within an 'Activity Layer'.