In Tracingstore, move temporary data from local cache to Redis

[fm3]

Temporary data (e.g. merged tracings for compound view) in the tracingstore is saved for some duration (e.g. 70 minutes as of #5246 )
All of it is lost, however, when the tracingstore restarts. This can lead to errors when viewing compound annotations for a long time. The design is from a time when compound annotations were always skeletons, so they were loaded to the client all at once. However, merged volume data is loaded as needed, so it is more important that the server keeps it long enough.

Moving this data to Redis may solve this issue, as it stores data across restarts.

A different approach would be to actually persist this data in fossildb and mark it as a snapshot.