RFC: Support a federated timeseries

[shankari]

From #851 (comment)

I believe that the correct long-term solution is to create a federated wrapper that can read entries from multiple programs.
If/when we create an overarching OpenPATH database that tracks that programs that we have hosted, programs that we are hosting, and generates the "DOE dashboard", we would be able to use it as well.

This wrapper should follow the current Timeseries interface; maybe closer to the AggregateTimeseries than the regular timeseries. Note that we can also create implementation(s) of the Timeseries that work with the Postgres database used in the secure portal, and any datastructures supported on Eagle.

Actually making the timeseries interface general will ensure that we can:

• do real-time federated analysis
• make it easier for others to reproduce our results on private data
• potentially support a switch to a more timeseries-centric database later

this federated approach is also consistent with the long-term vision of one database per user.