Collector service API and optimized NeXus files generation
This MR combines 2 different changes:
- A REST API to the collector service that allows monitoring the status, controlling the collectors, and updating the configuration.
- File generation in the collector service is now done on a process pool. The collector service can be configured to group several SDS events in the same file (affects all collectors running in the service). The files now include all metadata available in the SDS PVs generated by e3-ents
Also minor changes affecting variable naming.